One is a commuter bike piece of crap singlespeed (at least it's got 105 brakes that work) that I can leave locked up in the university overnight without much worry about theft. The next bike is my full-carbon Trek Madone 4.5 road bike, with nice upgraded Mavic Ksyrium wheels with the blade spokes. After that is a Giant Reign X1 "cross-country" mountain bike with 6.7" suspension in the rear, with some lightening done to the bike. Last but not least is my carbon Santa Cruz V10 full-on absolute top of the range 10" suspension downhill bike - which is actually lighter than my XC bike.
I try to ride at least once a week for a few hours on either the Trek or the Giant, reserving the V10 for uplift days at the local bike park or the annual trip to the Alps to take advantage of lift-serviced trails. The commuter bike is great for cycling in to meet my mates for lunch or for drinks in the evening as I won't drink and drive.
Biking is great. I get to see some lovely parts of the country, and the views at the top of the climbs are nearly worth it, but the descending really does make it all worthwhile!
Though I do need a secure shed instead of having the bikes in my kitchen..