Minor issue- .sln files created by Orcas Beta1 do nothing when double-clicked in Explorer. Hovering over the icon in Explorer shows "Version: (unrecognized version)". Everything works fine if you just open the solution file in Visual Studio.
Turns out the trick is in the comment on the third line of the solution file. For solutions created by Beta1 (and I'm assuming, anything older), the third line looks like:
# Visual Studio Codename Orcas
In Beta2+ solutions, it is:
# Visual Studio 2008
Change the line in notepad (or whatever), and all is well- you can open the solution by double-clicking in Explorer again.