Sheesh, I am a Camelbak ADDICT! I have a big pack one for long hikes, a moderate sized one for biking - road and mtn, a smaller insulated one for downhill skiing, and a fanny pack style for running and XC skiing. I think they're the best thing since sliced bread.

The weight has never bothered me when biking. I've also never noticed that I feel too warm from it.