My roomie is a vegan and recently read The China Study book. I just read the appendices because that seems to be where lots of figures and tables are. Just from reading the appendices I knew I didn't want to read the book because of its blatant biases and repetitive nature. I agree with everything in moderation. Also, books aren't peer-reviewed which in this case makes me think I should take it with a grain of salt. Although I think a lot of whats written is a good guideline for food intake.
Just on a personal note, when I exercise a lot I feel like I need to eat protein. I don't know if there is any science to back that up though.
I do agree that lots of vegans are healthy--like my roomie. It just isn't for me at this moment--maybe later on? who knows. I'm in an environmental major so there are lots of vegans surrounding me