This is probably the coolest thing I've bought recently.
Pain in the bum to install, but I suppose most people would geta locksmith to do it!
I often have friends/family staying, and I don't have to worry about either sending them a key or being around when they arrive - I simply tell them the code and they let themselves in.
If they're people I trust not to come in while I'm on the job, I enroll their fingerprints so they can come and go as they please. Magic. :-)