I've recently been working on a Windows Phone 7 application, and got thrown a small setback with the release of the beta version of the Windows Phone 7 tools. There are several breaking changes between the April CTP refresh and the beta version, which were making my life a bit miserable for awhile. I reviewed the release notes, but although the notes list the breaking changes, they don't offer any prescriptive guidance to migrating between versions. Fortunately, I found this great post from Jaime Rodriquez that does offer some guidance. If you scroll down, you'll see a section titled "Steps for migrating your code", which I found pretty helpful..hopefully you can use them too.