Here I am, sat at my desk, and I have literally NO work to do. All my projects are completed or awaiting input from other sources, over which I have not control or influence. There are no other little jobs I can do to help anyone else out. I have not user issues to deal with, or documentation to do. I can't just sit at my desk and read a book (as much as I'd like to) because that would look unprofessional. And there are only so many internet sites you can go to before you're all webbed out.
So - what would YOU do?