One more reason to add to the list -- if the router updates time via ntp and the time on the server is whacked, some users will temporarily lose wireless connections. I believe this is because the router's WPA/WPA2/etc. timers are set according to the time prior to the update. If the updated time is too far out of skew, this will cause the wireless connections to miss their authentication windows. The disconnection lasts for a couple of seconds. The log will show both the time update and the reauthentication.
Users that suspect that they're having this problem severely enough should set their router to use a single stable ntp server rather than a "pool" of servers.