ToastView allows to show UIToasts on the Iphone via Monotouch and C#

ToastView.cs

// Licence: MIT X11
// Note: This is an Objective-C to C# translation by using code from: http://code.google.com/p/toast-notifications-ios/
namespace Fusonic.Monotouch.Utils
{
    public class ToastView : NSObject
    {
        ToastSettings theSettings = new ToastSettings ();

        private string text = null;
        private UIView view;
        private int offsetLeft = 0;
        private int offsetTop = 0;
       
		public ToastView (string Text, int durationMilliseonds)
        {
            text = Text;
            theSettings.Duration = durationMilliseonds;
        }

        public ToastView SetGravity (ToastGravity gravity, int OffSetLeft, int OffSetTop)
        {
            theSettings.Gravity = gravity;
            offsetLeft = OffSetLeft;
            offsetTop = OffSetTop;
            return this;
        }

        public ToastView SetPosition (PointF Position)
        {
            theSettings.Position = Position;
            return this;
        }

        public void Show ()
        {
            UIButton v = UIButton.FromType (UIButtonType.Custom);
            view = v;

            UIFont font = UIFont.SystemFontOfSize (16);
            SizeF textSize = view.StringSize (text, font, new SizeF (280, 60));

            UILabel label = new UILabel (new RectangleF (0, 0, textSize.Width + 5, textSize.Height + 5));
            label.BackgroundColor = UIColor.Clear;
            label.TextColor = UIColor.White;
            label.Font = font;
            label.Text = text;
            label.Lines = 0;
            label.ShadowColor = UIColor.DarkGray;
            label.ShadowOffset = new SizeF (1, 1);


            v.Frame = new RectangleF (0, 0, textSize.Width + 10, textSize.Height + 10);
            label.Center = new PointF (v.Frame.Size.Width / 2, v.Frame.Height / 2);
            v.AddSubview (label);

            v.BackgroundColor = UIColor.FromRGBA (0, 0, 0, 0.7f);
            v.Layer.CornerRadius = 5;

            UIWindow window = UIApplication.SharedApplication.Windows[0];

            PointF point = new PointF (window.Frame.Size.Width / 2, window.Frame.Size.Height / 2);

            if (theSettings.Gravity == ToastGravity.Top)
            {
                point = new PointF (window.Frame.Size.Width / 2, 45);
            }
            else if (theSettings.Gravity == ToastGravity.Bottom)
            {
                point = new PointF (window.Frame.Size.Width / 2, window.Frame.Size.Height - 45);
            }
            else if (theSettings.Gravity == ToastGravity.Center)
            {
                point = new PointF (window.Frame.Size.Width / 2, window.Frame.Size.Height / 2);
            }
            else
            {
                point = theSettings.Position;
            }

            point = new PointF (point.X + offsetLeft, point.Y + offsetTop);
            v.Center = point;
            window.AddSubview (v);
            v.AllTouchEvents += delegate { HideToast (null); };

            NSTimer.CreateScheduledTimer (theSettings.DurationSeconds, this, new Selector ("HideToast"), null, false);

        }

        [ExportAttribute("HideToast")]
        void HideToast (NSTimer timer)
        {
            UIView.BeginAnimations ("");
            view.Alpha = 0;
            UIView.CommitAnimations ();
	    RemoveToast();
        }

        void RemoveToast ()
        {
            view.RemoveFromSuperview ();
        }
}
	
	public enum ToastGravity
	{
	    Top = 0,
	    Bottom = 1,
	    Center = 2
	}
	
	public class ToastSettings
	{
		public ToastSettings ()
		{
		    this.Duration = 500;
		    this.Gravity = ToastGravity.Center;
		}

		public int Duration
		{
		    get;
		    set;
		}

		public double DurationSeconds
		{
		    get { return (double) Duration/1000 ;}

		}

		public ToastGravity Gravity
		{
		    get;
		    set;
		}

		public PointF Position
		{
		    get;
		    set;
		}
	}
}

I added support for multi-line toast in this gist if you want it:
https://gist.github.com/danmiser/5943610