Had a hard time looking for the way to setup Wifi on my PC-BSD 8.0 installation. After much navigation, I found it nestled within System Settings -> System Network Configuration.
So I did my configuration here and expected Wifi to connect instantly with no problems. And it connected, for at least 5 mins. then it cut-off and after a few seconds it connected again only to disconnect after 20 secs. (or less). In other words, it was giving me intermittent connection.