I'm not a high-level mechanic, but after I got hooked a few years ago, I decided that I wanted to have a deeper understanding of how everything worked, so I took a couple of the Park Tools classes, and then built a bike up from parts because I figured that I'd only understand my "dream" bike if I could experiment and try different stuff. I started out thinking that I would get a rusty frame from the Goodwill store, but I ended up buying a carbon fiber frame on ebay, than a full Ultegra gruppo from my LBS. I am really happy that I did.
I still refer to the Park Tools site or a book on occasion, but when something is wrong, I have an idea of what it is. It also gives me something to do when there's ice and snow on the roads <sniff>; I'm working on building up a fixie when I get the time.
I'm a little more constricted about whether to work on my wife's bike or not. Last year, I put the rear wheel back on a little crooked which caused it to rub against the brakes - she was not happy
