create_activity.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Newtonsoft.Json.Linq;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {

        static void Main(string[] args)
        {
            //The service we want to call
            Uri uri = new Uri("http://seesmic.demo.exoplatform.org/rest/private/api/v1/social/portal/people/john/activities/?format=json");
            string username = "john";
            string password = "gtn";
            WebClientHelper helper = new WebClientHelper(null);
            
            //We want to create an activity, so we do a POST
            helper.Method = "POST";
            //We do the Basic authorization
            helper.Authorization = "Basic " + System.Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(username + ":" + password));
            
            //We add our callback for when the response arrive
            //Our call is asynchronous
            helper.RequestCompleted += delegate(object sender, RequestCompletedEventArgs e)
            {
                string dataFromStream = string.Empty;
                if (e.Error == null)
                {
                    Console.Out.WriteLine("Activity created.");
                }
                else
                {
                    Console.Error.WriteLine("An error has occured while accessing the server.");
                }
            };

            JObject data = new JObject();
            JObject message = new JObject();
            JObject entity = new JObject();
            entity["type"] = "note";
            entity["content"] = "my new activity";

            message["data"] = data;
            data["entity"] = entity;

            //We send our request with the new activity as payload
            helper.SendRequest(uri, message.ToString());
            //Just to block the program
            Console.ReadLine();
        }
    }
}

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Newtonsoft.Json.Linq;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {

        static void Main(string[] args)
        {
            //The service we want to call
            Uri uri = new Uri("http://seesmic.demo.exoplatform.org/rest/private/api/v1/social/portal/people/john/activities/@consumption?format=json");
            string username = "john";
            string password = "gtn";
            WebClientHelper helper = new WebClientHelper(null);
            
            //We want to get the list of activities
            helper.Method = "GET";
            //We do the Basic authorization
            helper.Authorization = "Basic " + System.Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(username + ":" + password));
            
            //We add our callback for when the response arrive
            //Our call is asynchronous
            helper.RequestCompleted += delegate(object sender, RequestCompletedEventArgs e)
            {
                string dataFromStream = string.Empty;
                if (e.Error == null)
                {
                    dataFromStream = GetDataFromStream(e.Response);

                    //We parse the response in json
                    JObject feed = JObject.Parse(dataFromStream);
                    //The response is always in the data
                    //we are interested by the list of activities, so we go directly to the items
                    foreach (JObject entry in ((JArray)feed["data"]["items"]))
                    {
                        Console.Out.WriteLine((string)entry["authors"][0]["name"] + ":");
                        Console.Out.WriteLine((string)entry["title"]);
                        Console.Out.WriteLine();
                    }
                }
                else
                {
                    Console.Error.WriteLine("An error has occured while accessing the server.");
                }
            };

            //We send our request
            helper.SendRequest(uri, null);
            //Just to block the program
            Console.ReadLine();
        }

        static private string GetDataFromStream(Stream str)
        {
            byte[] buffer = new byte[str.Length];
            str.Position = 0L;
            str.Read(buffer, 0, (int)str.Length);
            str.Position = 0L;
            return Encoding.UTF8.GetString(buffer, 0, buffer.Length);
        }
    }
}

WebClientHelper.cs

using System;
using System.IO;
using System.Net;
using System.ComponentModel;

namespace ConsoleApplication1
{
    //from http://facebooktoolkit.codeplex.com/
    internal class WebClientHelper
    {
        public event EventHandler<RequestCompletedEventArgs> RequestCompleted;

        HttpWebRequest _webRequest;
        readonly Object _userState;

        public string Method
        {
            get;
            set;
        }

        public string Authorization
        {
            get;
            set;
        }

        public string ContentType
        {
            get;
            set;
        }

        public Uri RequestUri
        {
            get
            {
                if (_webRequest != null)
                {
                    return _webRequest.RequestUri;
                }
                return null;
            }
        }

        public WebClientHelper(Object userState)
        {
            _userState = userState;
            Method = "GET";
        }

        public void SendRequest(Uri uri, string data)
        {
            byte[] postData = null;

            if (data != null)
            {
                postData = System.Text.Encoding.UTF8.GetBytes(data);
            }

            SendRequest(uri, postData, "application/x-www-form-urlencoded");
        }


        /// <summary>
        /// 
        /// </summary>
        /// <param name="uri"></param>
        /// <param name="postData"></param>
        /// <param name="contentType"></param>
        public void SendRequest(Uri uri, byte[] postData, string contentType)
        {
            _webRequest = (HttpWebRequest)WebRequest.Create(uri);
#if !SILVERLIGHT
            _webRequest.KeepAlive = true;
#endif
            _webRequest.Method = Method;
            if (Authorization != null)
            {
                _webRequest.Headers["Authorization"] = Authorization;
            }

            if (postData != null)
            {
                _webRequest.ContentType = contentType;
                _webRequest.BeginGetRequestStream(BeginRequest, postData);
            }
            else
            {
                _webRequest.BeginGetResponse(BeginResponse, null);
            }
        }

        /// <summary>
        /// Writes post data to stream and begin to retrieve response from server
        /// </summary>
        /// <param name="ar"></param>
        void BeginRequest(IAsyncResult ar)
        {
            using (Stream stm = _webRequest.EndGetRequestStream(ar))
            {
                var postData = (byte[])ar.AsyncState;
                stm.Write(postData, 0, (int)postData.Length);
                stm.Close();
            }

            _webRequest.BeginGetResponse(BeginResponse, null);
        }

        /// <summary>
        /// Parses response from server and signals the async operation
        /// </summary>
        /// <param name="ar"></param>
        void BeginResponse(IAsyncResult ar)
        {
            Stream response = null;
            Exception exception = null;

            try
            {
                using (var webResponse = this._webRequest.EndGetResponse(ar))
                {
                    Stream stm = webResponse.GetResponseStream();
                    ContentType = webResponse.ContentType;

                    using (BinaryReader reader = new BinaryReader(stm))
                    {
                        var buffer = new byte[2048];
                        response = new MemoryStream();
                        int bytesRead;

                        do
                        {
                            bytesRead = reader.Read(buffer, 0, buffer.Length);
                            response.Write(buffer, 0, bytesRead);
                        } while (bytesRead > 0);

                        response.Position = 0;
                    }
                    stm.Close();
                    webResponse.Close();
                }
            }
            catch (System.Net.WebException e)
            {
                exception = new Exception("An unknown exception occured. Look at innerexception for details", e);
            }
            catch (System.Security.SecurityException e)
            {
                exception = new Exception("An exception occured while downloading data. Look at innerexception for details", e);
            }


            if (RequestCompleted != null)
            {
                RequestCompleted(this, new RequestCompletedEventArgs(response, exception, _userState));
            }

        }
    }

    class RequestCompletedEventArgs : AsyncCompletedEventArgs
    {
        public Stream Response
        {
            get;
            private set;
        }

        public RequestCompletedEventArgs(Stream response, Exception ex, Object userState)
            : base(ex, false, userState)
        {
            Response = response;
        }
    }
}