I installed the Visual Studio 2011 Developer Preview on one of my machines, as it is supposedly safe to install side by side with Visual Studio 2010.
One of its supposed features is its ability to open Visual Studio 2010 projects/solutions without modifying them, which can then be re-opened in Visual Studio 2010.
It turns out this isn’t always the case, though I’m not sure why.
I have a solution that is (more or less) a silverlight application, and it simply won’t open the web project that hosts the silverlight app. When the solution is opened, it says it needs to convert that project (though it doesn’t really say what it needs to convert), and then it says it is unavailable anyway.
I installed the preview on a 2nd machine and got similar behavior.
Keep in mind that (minus installation time), I spent a grand total of about 15 minutes playing with it, so there might be some workarounds.
I might try it out on a 3rd machine (I’ve got a lot of them lying around) if I find more time.