I know that the Admins have a to-do list longer than Britney Spears' prescription drug history, so I have come up with a way to annotate during a game until they can work one in that will be much smoother.  It's basically creating a draft blog post (and therefore private) with a chessboard inserted, but if you are interested in the details, you will be rewarded with lots of colorful pictures and witty banter....

http://blog.chess.com/KnightNotHorse/annotating-during-a-game