Bwild: pokerstars and fulltilt allow 3 per hour.... I think that is very reasonable.
While this is very reasonable for Full Tilt and Stars, with their fast pace tables, I think it'd be OK to have a tougher limit here at BrainKing, but not less than once per hour. And maybe 90 minutes for pawns or something.
(hide) If you want to play a game with an opponent of a similar level, you can define a required BKR range for a new game invitation. Then nobody with a BKR outside this range will be able to see/accept it. (Katechka) (show all tips)