I have four, at present. The FG/SS gets used for pootling around town, going to the pub etc. and for hill repeats when I want to do some interval training. The tourer gets used for touring, obviously, and about once a week for carrying groceries. The roubaix-style carbon road bike is the most heavily used, especially for long distance rides and sometimes for light touring - if I'm only going to be away two or three nights and am not camping I can get all I need into a saddlebag. The more aggressive carbon road bike - a Giant TCR - gets used when I want to keep up on group rides and now that I am entering my second childhood, will from next spring be used for racing.

I don't have much trouble giving them all a fair bit of use, my mileage this year will probably top 10,000. I have to keep stopping myself from going out and buying a CX bike. I really don't need one...