How many bikes is it right to own?

I'm not enough of an expert to know how many truly different BMX bikes there are, but I had a race bike and a dirt jump bike at 15 & 16, and naively assumed I could ride street/skate park/half pipe on the dirt jump bike, although I had toyed with a separate entry for flatland. I'm surprised that nobody has insisted on adding a 29er to the collection yet.
ah you need 96er and 69er (childish giggle) hmm what else. . . have we covered tall bikes?