GuidEncoder from http://madskristensen.net/post/A-shorter-and-URL-friendly-GUID

GuidEncoder.cs

// credit: http://madskristensen.net/post/A-shorter-and-URL-friendly-GUID
using System;

public static class GuidEncoder
{
 public static string Encode(string guidText)
 {
  Guid guid = new Guid(guidText);
  return Encode(guid);
 }

 public static string Encode(Guid guid)
 {
  string enc = Convert.ToBase64String(guid.ToByteArray());
  enc = enc.Replace("/", "_");
  enc = enc.Replace("+", "-");
  return enc.Substring(0, 22);
 }

 public static Guid Decode(string encoded)
 {
  encoded = encoded.Replace("_", "/");
  encoded = encoded.Replace("-", "+");
  byte[] buffer = Convert.FromBase64String(encoded + "==");
  return new Guid(buffer);
 }
}