I actually talk quite a bit about wifi and security (and even in connection with Facebook) in the class I’m teaching this week (it falls under the “how to keep your private life… private” section…)
If you use facebook, make sure you change the security settings. The default behavior is over http and this Wi-Fi sniffing app (facesniff) for Android is gaining a lot of traction. It builds a quick ‘hit-list’ of usernames/passwords it has gathered as folks login with their mobile phones or other devices over wi-fi. Then it builds a hyperlink style list for someone to login to your account instantly after it is captured.