I've been doing a lot of Silverlight lately for a couple of projects. I upgraded them to the new Silverlight using the Visual Studio upgrade wizard that started automatically. It all works fine other than the minRuntimeVersion attributes on HTML pages that reference Silverlight xap files.
The problem is that if the Silverlight control was compiled under version 3 and you specify the version 2 runtime in minRuntimeVersion, you get an ugly error and download instruction:
If you update the minRuntimeVersion, then you get a much more user friendly version:
For the record, the old minRuntimeVersion was 2.0.31005.0 and the new runtime version appears to be 3.0.40624.0