NUnit to VSTS Conversion in Beta 3/RTM
I recently tried to convert some NUnit tests to VSTS using Jim Newkirk's converter posted on GotDotNet. It had been awhile since I tried it and I had forgotten an important detail... The add-in is based on the Guidance Automation Extentions which were previewed against Beta 2 and haven't been updated yet. That means you can't use the converter on a VSTS Beta 3 Refresh/RTM setup.
I spent about an hour and successfully converted the test project manually. It would've taken about 10 minutes if I had just followed the directions that Susan Entwisle posted in her blog.
If you do decide to convert NUnit tests to VSTS, don't be afraid to do it manually. The process is relatively painless with strategic use of Search/Replace over the entire test project.