OK, so loads of you are going to know this already, but if you don't is useful!
To comment the currently selected text, press ctrl k, followed by ctrl c.
and to un-comment the currently selected text press ctrl k, followed by ctrl c
Visual Studio uses the correct type of formatting no matter which type of document you have open (e.g. style sheet, c# file, html etc)
I use this all the time, and its something you might not have come across!
You can find a complete list of shortcut keys for visual studio here
Know any other time saving hints, let me know!!