My (admittedly cheap) wireless router can be picked up in the next room. Beyond that, you're in the lap of the gods. I originally put it down to cheapness. However last year, I acquired an old Belkin router we used at work. I *know* this routers signal managed to push through 2 buildings to get picked up in the office we had next door to us - about 100ft. Yet using that at home was no better than the cheapie.
The only thing I can think is our internal walls are proper brick (built in 1963) which strangles the signal. But that said, the signal was punching through 5 brick walls at work.
WiFi is great for convenience, and simplicity. But I would never *rely* on it as a primary network path.