In a discussion Alex started Compare community extensions, he mentioned a primary requirement of extending the User Object. Sometimes, that's all folks are looking for and adding a community extension can be overkill.
I wanted to point out Kevin Devine UserMeta extension. Check the Readme in his download for all the instructions you need. I have a video that shows how I used this feature in the SxSW entry, too, which you might find helpful.
It's a good example of a "building block" piece of software that works with other solutions.
Pretty cool - I think yes this goes pretty much into the direction I was looking for. Also the ideas of having just a simple plugin that you hook in is pretty much what I had in mind too.