When I was doing my CFL Teardown I mentioned that I thought the PCB would make a cool keychain. It does. I have had it on my keys for a little while now and it works quite well at helping me find my keys without getting in the way. I like the side with the components silkscreened on, most people like the green side with the traces.
To make it work as a keychain I had to widen out one of the holes to fit the key ring through. There are a ton of ways to do this, but I happened to have my Yankee Drill sitting on my counter as I was working, so I used that. Next I wanted to take off the excess solder so all the holes would be visible. I was feeling lazy so instead of using a solder sucker I just used solder wick. Once I was happy with the amount of solder I had left I put the keychain in my toaster oven to round off any sharp bits of solder that were left over. This made the board a bit discolored, but it also kept me from cutting myself when pulling my keys from my pocket.
After a few weeks using it the only problem I see is that I am slowly wearing the hole larger. I figure that in a few months I will wear completely through. I could cover the whole thing in a clear epoxy and it would probably last much longer. Probably I will just take apart another broken CFL and use the PCB again.
What made you think of using the PCB for a keychain?