There was a slashdot article a few months ago about the Defcon convention in Nevada i think it was and one of the challeneges was longest range for wifi. The winner got somthing like 11 km's using 2 usb wifi adapters a couple very large satallite dishes. At 11 km's (or whatever it was) they actually ran out of road. The signal strength was also supposed to be something comparable to two laptops with internal wifi sitting next to each other. So its all about focusing that power.