well, the subject pretty much says it all. used to be airport activated when the computer was turned on and stayed on until it was turned off. now, when i login i have to select my network from the airport menubar item each time and when i logout, or go to the login window, it turns off.
i have tried playing with the network settings, including checking "automatically join this network" and have done the airport setup assistant again to no avail.
i noticed the change after doing a security update. i have a belkin 802.11G card on a pismo, fwiw.