I've been learning about them and their various applications for a little while now. Seems they've been in use in Japan for quite a while, and now they're making their way to the U.S.
You can do quite a bit with these things: Simply drop a URL or a text message, for instance, or embed a bunch of contact information. Or an ad, or a coupon, or information about a painting at a gallery.
And the fun part is any smart phone with an auto-focus camera can read them. BlackBerry Messenger 5.0 and newer even comes with one built-in, if you're only including your BBIM or a URL. There are other apps out there that will read more complex messages.
I've been using
I wouldn't know what to get for the BlackBerry or Palm, but I know there are apps out there. Stick a link in comments if you're using a good one.