WiFi security onboard?

[elf]

I have read a lot of posts here about cruisers using open WiFi connections in various marinas, anchorages, and so forth. What is to prevent someone from stealing your email password and other personal information over such an insecure connection? I realize that some sites, say financial institutions, should encrypt the information sent, and I know that https: sites are used for most e-commerce whenever credit cards are entered, but I'm not sure that userid/passwords are encrypted in all cases; for instance, when using Outlook Express to access email. And I've heard about people being able to steal information by sniffing WiFi connections, but I am not sure how this works.

How secure is it out there? Are there precautions that can be taken to minimize the chance of my information being stolen if I use a WiFi connection at sea? What do you all do to practice safe computing while cruising?

Thanks!
Elf