Please forgive the self promotion, but I made a macosx app called memoryIO.
It takes a picture whenever you open your Mac and puts it in your My Pictures directory.
I’ve been using the awesome open source scripts sleep watcher and imagesnap to take photos of myself for more than a year, and friends have been doing it longer.
Usually I have trouble convincing friends the value in QS tracking, but one thing they always enjoyed was seeing how I changed in pictures, who was next to me, where I was, etc.
Pictures are a bit of a trifle, but it seems like a fun and effective QS gateway drug.
I’ve combined the scripts into an open source MacOSX app. Again, its free and open source.
Please check it out http://www.memory.io