The idea is simple enough, there are a few free apps that can read/write tags that work quite well. If there was a way to sniff the tag read event and have its ID or contents trigger an action it would be awesome. I assume integrating true NFC reader communication might be tricky but the reader reads weather an app is even using it so I bet theres some event somewhere that could be grabbed with an applescript or something.
Off the top of my head you could
Tap keys/phone to unlock computer
Tap a sticker on a flash drive to launch a specific backup/sync script