Most of the time I'm using fullscreen in Visual Studio, however when VS is in fullscreen the standard toolbar buttons are also hidden, which is fine. The only problem is that the comment/uncomment buttons are also hidden. After a bit of searching through the documentation of VS 2008, I found what I was looking for: The short-cut keys for comment / uncomment - and here they are:
Press Ctrl-K, Ctrl-C = comment code block.
Press Ctrl-K, Ctrl-U = uncomment code block.
Having access to the comment/uncomment feature of VS 2008 in fullscreen using the above keyboard shortcut is really nice! - Enjoy! :-)