I used to have an rfid chip implanted in my hand. I had all these ideas of what I was going to do with it - log on to my computer by putting an rfid reader in my keyboard, build a magic 'touch the wall and music starts playing' thing etc. All of them turned out to be very boring and useless in practice. Logging into my machine - meh, turns out that it takes longer for monitors to come back on than to type the password. Building (useful) user interfaces based on rfid is very hard and doesn't add anything over a regular proximity sensor. The only idea I have left is that in my current house, I have a place where I could put an rfid reader so that if I'd get a chip implanted in my gluteus maximus (my butt, essentially) I could activate an automatic door opener by bumping into it when I have my hands full. I just can't motivate myself to set this up and discovering again that it's a dud in real life.