I have 4 and I ride them all each year. 1 road bike, 1 back up or "rain" road bike that has rock solid wheels for the off season bad roads, 1 heavy steel touring bike for day trips, sightseeing, generally whenever I feel like going slow and the occasional weekend overnight trip, 1 hybrid for towing the kids tag along and trips to local stores, and snow riding. I can easily find another category to fill with a 5th bike but quite honestly I don't want another bike to compete for my money. It seems like I'm always needing something; brake pads for this one, cable housings for that one, worn bottom brackets, wheel spoke tensioning, the list goes on and on. It almost feels like I'm working for my bikes. That's why 4 is my self imposed limit.