I picked up a packet of 15 tags of assorted sizes from here
for $15.95 plus shipping to the US. Then had my daughter stick them in an envelope and send to me.
Anyway I have been playing around with them using NFC Task Launcher.
I haven't done much but so far I have put one in my car dock and when I put my GN in the dock it fires up Car Home.
And I have one on my BT speakers at home and when placed on the speaker, it turns on BT, connects to the speakers and then fires up Google Music. To get the phone to connect to the speakers I had to use Bluetotth Auto Connect from the Play Store. That app connects to the last BT device connected which wasn't what I wanted since that is normally the head unit in the card (phone and music) But the author kindly changed the app so that you could set which BT device to connect to when BT is turned on and keep it to that device.
I now have a further 13 tags to play with. Now looking for applications to use it usefully.