I live in a geekhouse, which is shared housing situation that is more social than an old-school boarding house, but less "into each other's business" then being "family". This kind of shared housing is a model that is popular with the geeky set, especially in my neighborhood in Seattle.
One of the problems with this situation is physical access control, that is, locking and opening the front door. There are a number of people who live there, a number more who have "walk in at any time" social status, plus out of town guests and visitors, and so forth. Keeping track of who has a key and recovering guest keys is awkward at best. And rekeying the locks would be very annoying.
I've been reading about RFID, MIFARE, and the Maker revolution for some time, and have decided to actually Make something interesting and useful. I'm building a way to open the door with an RFID card and/or a biometric.
So many people immediately say "but, it could get hacked!". And my response is: a break-and-enter criminal type would just break the window, and any hypothetical black-bagging spooks would just pick the lock. So adding this will not lower the actual security, and would increase it by decreasing the actual physical keys "out there".
So I'm starting with this project. Then I will add a fingerprint reader, and then run a link back to a server with a database, either over ethernet, zigbee, or some other link. I will use a digital output line to drive a transistor that will drive a relay that will drive a standard off-the-shelf electromagnet door striker (the thing that goes BUZZ when you get buzzed in). All of this stuff is off-the-shelf from places like AdaFruit.
Then I can start doing cool stuff on the server side, such as do the access lookup via RADIUS or LDAP, so existing scalable and federating identity systems can be used, across multiple units. And set it up so people can choose to do a Foursquare checkin when they touch in.