It's all on their secure blah blah blah, but yes, it is REALLY sweet. I LOVE being out and about, wanting to buy something, and checking my balance RIGHT THERE to make sure I have enough dough. Or, waiting to see if a paycheck has gone through, or waiting to see if proper funds for bills have been taken out yet, etc. You can check your balance, pay bills, even transfer funds. My mobile banking has saved my ass many many times and I love it sooo much.
And if you're nervous someone would snag your info out of the air on WiFi, just turn the WiFi off and use 3G or EDGE.
Seriously, though, I will never be able to have a phone that's not an iPhone again. The amount of amazing shit this thing can do, from the power it packs to the built in features to the app store, I would die without it. I have an app, where if I see something in the store, I can take a picture of its bar code, and it'll scan it and show me A) all the sites online that carry it and B) all the stores in my area that sell it and C) where the cheapest price is. Holy shit, mind blown.