This seems superfluous! Too many options are cluttering up the game pages already, and there are plenty to work with. Would it not be more practical for any given player to make a written or mental note of which opponents are currently on line?

Players online changes continually. Mental or written notes are hardly practical. I would suggest some sort of indicator, similar to the asterix used to show tournament games would suffice.

I agree Grenv. That would also work fine.

Pioneer: not superfluous at all. How would one more option on the Move and Go To drop down menu be cluttering? If anything on that menu is "cluttering" it would be the Move and go to Discussion Board.
Anything that limits the # of pages to be loaded, would be a good thing, in my mind. As it is now, I am constantly going back and forth between "On line opponents" and my main page, then the specific game page.
If it is something not possible, then I can certainly live with it. It is simply a feature I would like to see.