1. Giant TCR Aero w/ durachee: Race (back in the day it was set up as a TT bike)
2. Trek 5500: Race (once upon a time) and group rides
3. Trek XO1 Cyclocross: Cyclocross racing and my everyday commuter
4. Trek 9.8: All around fast as hell mountain bike, never gets ridden anymore but hopefully one day
5. EAI bareknuckle: Not completed yet, but soon to be fair-weather commuter and race bike
6. 1947 Schwinn Tornado: Has 3 big ass baskets for grocery-getting
7. 1973 Schwinn Twinn: Tandem bike bought when I had a significant other

I don't think you can have too many bicycles. I think the longer you ride, the more you see the benefit of having specialized bicycles for various types of riding. In a dream world I could very happily have 3-4 road bikes. One for road/climbing races, one for Crits, one for the rain, one (steel) for training. I could then happily have 2-3 track bikes. One commuter/beater, one race-only machine, one pursuit bike. At that point I could also say for mountain bikes: I'll have one hardtail for fast hardpack and lots of climbing, one XC-race full-suspension, and one all-mountain trail bike. I mean the list goes on and on, and they all have their benefits! I can justify another bicycle as long as it has it's uses. As for people with multiple race-bikes or multiple beaters... why not? So what if they are "collectors" AND riders? More power to em' !!
Sure, I could get along much better with one bike... but then my income would go towards something else like say... investments!? Who needs a retirement anyway, right?