I've sworn off stock bikes. For me, building has become integral to riding (building in this case meaning completely stripping old road bikes and retooling as a fixie--wheels from scratch are optional). It is the difference between accommodating yourself to a machine and accommodating the machine to you. Tinker, test ride, switch part, test ride--you get a feel for what you want out of a bike. Plus you end up with a closet full of parts for the next Frankenfixed. It is partly an issue of character (the bike's, not mine; I have none), part preference (all mine), part DIY spirit.