Per Session Static Variables

"The ThreadStatic attribute is what makes this work. The only gotcha so far is that this doesn't work in an ASP.NET application (Web/Webservice) as threads are reused for different requests, hence having the wrong ObjectRegistry serving the wrong user/session. The only solution I can think of for the time being, is having the ObjectRegistry detect if there's a HttpContext, and if so, subscribe to the EndRequest event of the associated HttpApplication and clear itself when the event fires."
[Yves]

Much easier solution for web apps than using ThreadStatic:

public class ObjectRegistry
{
   public static ObjectRegistry Current
   {
         get
         {
               	if(HttpContext.Current.Session["__objectRegistry"] == null)
               	{
			HttpContext.Current.Session["__objectRegistry"] = new ObjectRegistry();
               	}
		return ((ObjectRegistry)HttpContext.Current.Session["__objectRegistry"]);
         }
   }

   // ...
}