Adafruit is one of a few companies that has been chosen to test the Square dongle that automagically takes credit card payments on any iPhone. Even though we got to see it in action at Macworld, I think every look we can get at this thing is worth it, considering just how darn revolutionary it seems. The video on Flickr shows just how quick and easy it is -- just swipe the card, and sign with your finger on the iPhone's screen.
I haven't bothered carrying cash for a few years now, and something like this only makes it easier to not only take payments for vendors, but for me to pay. Hot dog guy needs a few bucks but doesn't have a landline connection to run a credit card on? No worries, just swipe and done. Want to give to the Salvation Army guy over the holidays but don't have any money left in the wallet? Just swipe and done. Word has it that the transaction cut will be 2.9% (though the video above shows 3.5% -- maybe you can change the percentage depending on circumstances), but odds are that in most cases, the convenience will be well worth it.
The whole program's still in beta, but it probably won't be long before you'll see (and maybe even use) one of these out in the wild.