Among the unwritten rules of cycling (they are written here for the curious) is the answer to an existential question: how many bikes should I own?
"The minimum number of bikes a cyclist should own is 3. The correct number of bikes should rather be expressed as n+1 , where n is the number of bikes currently owned. This equation could also be expressed as s-1 , where s represents the number of bikes resulting in separation between you and your partner."
http://www.velominati.com/the-rules/#12
It's clear that the people who wrote these rules are passionate. A minimum of 3 bikes!? We bet many of us dream of having such a well-stocked stable! But seriously, can we be content with just one bike? How many times have you stayed home for fear of damaging your precious carbon toy? How many times have you given up a forest ride for lack of adequate tires on your steed?
The reality is that once you're bitten by the cycling bug, you always want more! Whether it's for commuting to work, mountain biking on the weekend, or family rides, chances are you'll want a different bike for each activity, and if you have the right tool, you'll always be better served.
The answer to our question would therefore not be, as the Velominatis suggest, more and more bikes until your partner threatens to leave you. Rather, an adequate bike for each of your needs. And if all your needs are met by the same steed, you certainly have more space in your garage than I do!