Scott mentioned on twitter a great post on using VS2010 code coverage with ASP.NET unit tests with the following comment.
So I figured I would work up a quick post on using Gallio with the code coverage features (and thus MbUnit, NUnit etc).
Using Gallio with the VS2010 code coverage features is exactly the same as you would use MSTest. Just enable the code coverage collector.
Select the assembly you want to profile (double click the collector to do this)
Run your test
Right Click and select code coverage.