For starters, don't use a public computer such as at an airport, hotel, or an internet cafe. As long as you connect with your own, you're swimming in the same ocean whether you're in Ohio or Thailand.
(OK, so Ohio and the ocean don't exactly go together. )
I take these precautions and feel comfortable doing financial transactions online, including over wireless. Definitely agree w/ alvarezg - don't ever use public computers for this.
I use my own computer (laptop) with internet access via a Verizon aircard (will not use wifi for secure transactions) and have almost all of my financial stuff with Etrade set up with a security key (gives a 6 digit number that changes about once per minute and is required for logins). Perhaps that's a bit overboard but it feels secure and don't want to lose my retirement to some ace hacker in a third world country.