Any pointers for the documentation on the new features of mbunit v3?
The Wiki and the API documentation are the most reliable sources of information for Gallio and MbUnit. Some blogs are interesting to read as well (mostly maintained by contributors):
The Wiki is certainly more convenient to read but is still a little sparse. However, the Gallio team members put a lot of efforts in it. They add new articles on almost a daily basis. If some people are volunteer to help, they are welcome to drop a line here.