My own perfect number is the point where the number of bikes I can (and actually will) use for different purposes meets the number of bikes I am capable of maintaining. Too many bikes means too many parts to keep track of.

I have three at the moment, a do everything commuter, a road bike and a mtb with a front shock. I would like a dedicated winter bike, but I've tweaked the commuter just right and prefer using it for everything. The only hassle is the segue between seasons and judging when to switch tires, so I end up riding for longer on studs just in case. So my perfect set-up would be two identical commuter bikes, one for winter and one for summer :-) A full suspension would be great fun too, but that would mean I'd never use the other mtb.

I'm sure I'd love having one of those transport bikes as well, but then, I do have a trailer and the attachment thingy permanently on my commuter so it's not very hard to go shopping as it is.

eta: which reminds me - I finally cannibalized the parts off my old and beloved Trek "loaner bike" and threw the frame away, because nobody was ever going to use it. I shall have to edit it out of my signature.