I have two, my Kona Dew plus which is my "town" bike and used to commute and haul kids around and my beautiful f.s. mtn bike, a Specialized Era.
My partner has no less than four and is awaiting the arrival of the fifth, a custom steel commuter.
This means that I am due for a couple new rides (the next purchase will be a Luna for me).
In our house the appropriate number of bikes to own is n+1, where n is the number currently owned.
We always check with the other before bike (and other big) purchases, because our bikes are rather expensive and we like to involve each other in the shopping.