i live in london so my commute is actually quite fun - dodging cars and pedestrians, small children and animals...
well, maybe not. but it is good fun, a little bit of exercise in the morning/warmup for the gym sesh pre-work.
and if you know london, you know that the tube is ridiculous - my annual ticket would cost around £1.5k; i would have a very unpleasant journey, crammed into a carriage with someones armpit in my grid; in summer the journey would be worse as the carriages seem to heat to dangerous levels; tube delays and problems are a fairly common occurance
my bike? £600 a few years ago + £200/300 on bits and pieces throughout the year + £100/200 a year on servicing (and i think these estimates are quite generous!)
plus i can shower when i get in the office.
plus i know (to within +-5 minutes) when i will arrive at the office.
it really does make sense!