Update: Great post by Julian Dominguez from the Prism team here that tells exactly what files changed in case you just want to update those in your source control: http://blogs.southworks.net/jdominguez/2009/02/prism-20-download-bits-refreshed-whats-changed/
In case you have already jumped on downloading Prism 2 (Composite Application Guidance for WPF and Silverlight) when it released about a week ago, time for you to go get some fresh bits. There were a couple of minor issues that have been fixed and the download links now have the updated code behind them.
So remove what you have for Prism 2, go to the download links and get the latest.
In WPF the main thing affected was that certain containers, TabControl in particular, did not bring their View to the foreground with an Activate call on the region. There was also a build issue for Silverlight projects that was fixed.
So go get yer fresh hot bits!