Web Parts Personalization data in Beta 2 serialized Nullable<T> with a slightly different format than the RTM version of the framework.  There is now a publicly available tool that will check personalization blobs in the personalization database for the old format, and will edit the blobs to conform to the expected format in the RTM version of ASP.NET 2.0.

The download link for this tool is:

http://download.microsoft.com/download/6/3/8/638657b9-e218-4372-b65a-ffd5cef2f5c3/PersonalizationConverter.msi

You only need to use this tool if you run into deserialization errors on the released version of ASP.NET 2.0 when attempting to deserialize personalization blobs from Beta 2 that contained Nullable<T> data.  If you have not encountered this problem, then you do not need to use the tool.