For reference on the PS3, the WiFi antenna and bluetooth antenna are located on a small board that is at the front of the machine on the left. On units with the card reader, it's under the flat plastic when you lift the lid to get to them.

Maybe placement is affecting it somehow. I haven't used the wireless on mine personally, as I have a small hub and the powerline ethernet adaptor behind the home entertainment center to connect the PS3, Wii, 360, ReplayTV and AppleTV units.