There's a lot of stuff out there on configuring the GuruPlug as a wifi client, but most of it is either pretty involved or kind of hacked (throwing random commands in rc.local and the like). I wrote up a tutorial (
http://blog.zortrium.net/archives/67) on getting client mode working reliably and cleanly (through the regular /etc/network/interfaces file) that shouldn't take more than about 5 minutes to follow. I'm posting it here for anyone to use and also for any feedback on good client setups people have.