I played about with Tasker and managed to do some fairly cool stuff. I can now make bumping a tag do different things based on variables like location, time, date and even things like air pressure and strength of magnetic fields.
A simple example:
I can bump my phone on a wristband or necklace when I’m at home, and my phone will fire up navigator so I can plot a route. When I’m not at home, it will fire up navigator and automatically plot a route home.
Or, more interestingly, when I’m at home it will toggle wifi or something and when I’m somewhere I don’t know – somewhere not a place I’ve specified such as work or my friends’ houses – it will plot the route home.
If you’re interested in this kind of thing, check out this guy: http://boingboing.net/2013/06/24/implanted-invisible-headphone.html
He has a magnet implanted in his ear which can be used as a speaker via a coil he wears round his neck. He has very cool ideas about what to do with it, including echolocation and super-hearing. This could work with NFC tags too. Since my phone can detect magnetic field strength, he could hold it to his ear and bump it against a tag on his other wrist and that could trigger, say, playing or stopping music. If the phone wasn’t to his ear, bumping the same tag would do something else.