I don't say that you should always be overly concerned when using a wifi. Though, you should pay attention at which wifi you log on and what services you access while doing that.
Do you really need to check you email on a public wifi? If it's not necessary, then just don't do it. It's the small things. Sure you can take this into the extreme (which is never a bad thing in this case), but even if we don't, then we should not teach people that every public wifi is perfectly fine. Please remain thoughtful.