The good news is that my GotDotNet sample on async callbacks in ASP.NET 2.0 runs fine under the CTP release of ASP.NET 2.0 (v2.0.4031). The bad news is that there has not been any changes made to the RaiseCallbackEvent method in the ICallbackEventHandler interface (which I considered to be a bit limited). Speaking to Darren a while ago, he thought that I might be the problem rather than the method signature. He said it was fairly consistent with some other method signatures on similar interfaces in System.Web (although I can't recall which ones).
1st of April has come and (almost) gone. I fought hard to resist the temptation to post a story with the following title “Porting Cygwin to Java so it can run on Linux”, with a message explaining how I was starting a new project to port cygwin to Java so Linux users could benefit from a powerful shell and good command line tools. I'll have to think up something better for next year.