The Wall Street Journal's Walt Mossberg has some sage advice here about what you should and SHOULD NOT do on public Wi-Fi networks. The reality is that it's easy to compromise your machine and your data on these networks. A bad guy can set up a fake access point, or compromise your internal routing tables, or download a Trojan onto your machine.
I know, I know - what else are you going to do at Starbucks? You've got a couple of options. Personally, I use a 3G EVDO wireless service from Verizon (Sprint and AT&T also have competing services) to provide my connectivity when I'm out of the office.
Yet, the reality is that I do connect on some public WiFi networks. It's not frequent, but it does happen. To protect those sessions, I use a public VPN service to encrypt the traffic from my machine to the Internet. The service I use is from WiTopia. There are a bunch of other one's and you could also set up a proxy server on your own network if you are technically-inclined.
The main point is to reiterate Mossberg's view. Don't do anything sensitive on a public WiFi network. It's bad for the health of your identity.
