Capes would be nice if the're full length, can cover you completely when you're standing still and flow behind you when you move at differnet rates - I mean billow when you walk and flap straight out when you run. In other words if they look like real capes.
If they're plastered to your back like the capes in WoW or stiff as a board like City of Heros then... meh.
Honestly, I don't think we're to the point yet where real looking capes are possible in video games.