It's not possible in Live Chess, although it would be very useful. (The only way to do it in Live Chess right now is to type the opponent's name in the Search field of your Stats page manually, which is too much hassle to do regularly.)
Have I played this person before?
Looks like this feature has just been added in today's site update? That's nice! Now when you click the opponent's name, when his page opens in another tab, there is your win/loss record against him under his name. It would be nice to include this information directly in the "game announcement" window at the start of the game, though (along with points to win/lose in the game about to start).
Is there an easy way to see if I have every played someone before in Live Chess (blitz)? I would like to be able to do this after we are paired, which is right when the game starts, so I'm looking for a quick way to do it.
I thought I remembered seeing a little note about my games against an opponent when I view their profile, but maybe that is turned-based? Thanks for any help.