Jeff Wilcox has published a simple tool that he uses to round-trip Silverlight solutions and projects between Visual Studio 2008 and Visual Studio 2010 Beta.
I wrote a tool last month for round-trip converting Silverlight-specific solutions and .csproj files between the versions, and want to share it as-is, with no warranty, hoping someone finds it useful.
Here are two potential solutions for dealing with the conversion issue, actually the second builds from the first.