Having spent a few years in a call center doing tech support in a former life, I would never recommend you use public wifi for anything you're be concerned about being stolen. It's ridiculous how easy it is to "hack" a wifi (even one that is "secured") if you know what you're doing. 9 times out of 10, you're alright because no one else in that library or coffee shop with you has any malicious intentions - but that one time when you happen to be in the wrong wifi hotspot at the wrong time is all it takes to make a big mess.
