Just one tip in case it happens to you: If you're updating to the latest .NET FX 3.0 builds, and you're using Windows Workflow Foundation, make sure you update any tracking and persistence databases you're using to the latest schema [1].

I ran into this with a Tracking database I had created incorrectly with the WF Beta 2 schema, and was causing the WF runtime to hang/freeze as soon as I enabled the SqlTrackingService.

[1] You'll find the necessary SQL Scripts to create your databases in the "%windir%\Microsoft.NET\Framework\v3.0\Windows Workflow Foundation\SQL\EN" folder