Why? I was riding a MTB (to and from work) and wanted something lighter. I purchased an older road bike, nice yet needed a few upgrades. With the internet at my fingertips, I wanted to try wrenching and stumbled upon the wonderful site of Sheldon Brown. He made me want to build one (I say build, it's really taking apart and changing a few things) and it happened. My commute became much better.

I guess that answered the second question as well.

I have one MTB, one fixed gear conversion (which just went on a wild ride without me in the saddle) and an old ten speed. Also a frame that is about to be built up.