My Pbook stopped automatically connecting to my regular wifi networks. Is it possible to set certain networks as "trusted" and let OS X connect to those automatically?
In the Network pane of System Preferences, under the AirPort section, there's a drop down list that lets you either connect automatically to an available network or only to preferred networks. What does yours say? There should also be an Options button at the bottom. What's checked or unchecked in there?