about 20 feet or so so the ps3 can wire into your internet router. as in, no wifi. although there is wireless, but the only way to play "online" with people is via ps3 adhoc thingy majigger and some complicated computer thing i dont care to explain.
although you can play with people wirelessly, and if thats the case try being as close as possible with little obstructions like chairs and walls as possible to ensure the best connection.