I'm also having the same issue as reported, but can add another wrinkle into the mix, and perhaps a solution for others. I have two machines as follows:
Machine 1: Laptop running Windows 7 Pro Final, VS2008 Web, VS2010 Beta 2, Q3 2009 ASP.NET AJAX
Machine 2: Desktop running Windows 7 RC (Ultimate), VS2008 Pro, VS2010 Beta 2, Q3 2009 ASP.NET AJAX
On Machine 2, I was having issues with intellisense in VS2010 after installing VS, then installing Q3, then opening an existing project in the new IDE. Resetting to default settings in the Import/Export settings dialog, and restarting VS fixed that problem. Hopefully that will help out somebody else (it was suggested on Rick Strahl's blog regarding js intellisense and just happened to work for this too).
Unfortunately, doing the same thing on Machine 1 does NOT work, but I'm guessing that there's got to be a setting somewhere buried in the VS 2010 options which will fix the issue; just not sure which one. If anybody has suggestions I'm all ears!