I am working on a control that passes a small amount of encrypted data in the url. No need to encrypt it while running under the local Visual Studio Web Server. You can check to see if 

System.Diagnostics.Process.GetCurrentProcess().MainModule.ModuleName

returns 'WebDev.WebServer.EXE'. Cool little piece of code. Full details on Steven Smith's blog:

http://aspadvice.com/blogs/ssmith/