Any data on the internet can be intercepted - phone calls, wifi, surfing the web, anything. And if you go outside a deep cave you can be hit by a falling airplane. I think the odds of being hit by a falling plane are just a little better. Unless you're doing things that aren't too smart to do on wifi - like going to your bank's site and putting in the login and password that would allow someone to transfer money from your account to theirs - no one is really interested enough in whether you get your news from AOL or Huffington to monitor your packets.
The only passwords I keep on a phone - and that's to sites like this, email accounts that aren't important, etc. - are encrypted with a duoble-military-strength encryption. And if anyone wants to come here pretending to be me, I'm not losing any sleep over it.