I concur, 1 is not enough! Whilst my early cycling career (on shelf stacking and bar job wages) was limited to one bike...a 10 speed road bike for my 16th birthday, now that I have a little bit more disposable income (and a bike infatuation problem) I'm up to 4.
1) 140mm full suspension, ride everything MTB which I have used for everything from trail centre thrashes to C2C last Easter
2) SS 29er, built for winter but also used for commuting in snow and actually used in preference to the FS sometimes as it's just so much fun.
3) Steel framed, Campag clad retro road bike...that can hold it's head up with any of the carbon framed roadie boys round here!
4) Steel framed, fixed wheel road bike/pub bike/bit of fun...that used to be the 10 speed road bike of my youth.