I'm testing my existing apps in VS 2010, and ran into my first break. ASP.NET AJAX authentication support has changed.
Sys.Services.AuthenticationService.set_defaultLogoutCompletedCallback(OnLogoutCompleted);
This no longer works. "Sys" is defined, but "Sys.Services" is an undefined object. Does anyone have a quick pointer to the replacement functionality?
EDITED TO ADD:
I've marked this as answered, based on the information that ASP.NET AJAX has changed, and that the client-side AJAX is now separated from the Visual Studio 2010 and .NET 4 distributions. In itself, this is not sufficient for a successful migration, though. Among other things, the current MS AJAX beta does not support the extender wizard in the ASP.NET designer. Also, I haven't found a way to compile successfully with control extenders added in previous releases of ASP.NET AJAX. It looks like AJAX migration will be a tough area for ASP.NET apps in VS 2010.
Around VS 2010 release time, I hope to see a community wiki for migration tips and techniques.