Depending on your background you'll have different reactions to Free Wireless. Most people shout a quick whoopee, and plug right in there. However if your background is in IT security, you take a much dimmer view.
First of all there's the fact that a lot of the traffic you send down the wire can be intercepted ("sniffed") by people on the same network as you. The guy next to you in Starbucks could be snagging all your email passwords, for example. So at a minimum you need to make sure that you're using Secure email protocols (eg Secure POP on port 995 instead of port 110, and Secure SMTP on port 465 instead of port 25), and using https intead of http wherever you get a chance.