Only place I've seen these so far are in magazines. I've definately been impressed, but it will be even better if/when it gets widely adopted.
A shorter address to get to it on your phone is
http://gettag.mobi Direct link to the .CAB file (standard WinMo version, since the TP2 isn't in the HTC list):
http://download.microsoft.com/downlo.../TagReader.CAB
Justin