The keirin is meant to be about aggressive riding, with an unpredictable outcome. It was invented in Japan where they absolutely love betting on it. Apparently there's over 50 tracks in Japan.. A bit like greyhound racing I guess. I think the yakuza have been known to fix a lot of the races.
The rules are very tight over there - only certain steel frames and components are approved for the bikes. The idea is to make the bikes similar to what a state of the art track bike would have been in the 50s/60s and to level the playing field as much as possible.
The motorbike (or they use another bicycle rider sometimes) starts off around 15mph, and leaves track at 30mph. I guess it cuts down a lot on the slow game of chess that happens with a one on one sprint. But on the other hand, the race starts at a pretty high pace, and theres much more of them on the track.. So the strategy is different, you've got to see the gaps, position yourself and time your sprint.
My favourite form track racing is the elimination race, but I like keirin a lot too.. I'd love to be fit enough to compete in an amateur race. I did a couple of possibly illegal sprint races in the past (!) and did okay, getting to the semi final.. But you cant compare to a proper competition on a velodrome. Anyway, the point is, the buzz of sprint racing is absolutely fantastic.
I'm saving for a holiday in Japan later this year and hope to see some keirin races. I've only become interested in cycling the last 3 years ago or so, but it's a great world I think.