Camelbacks are WONDERFUL! I have 2, and I love them. You tend to drink way more water, hence you're better hydrated in general. Then you can stop if you want to stop, but you don't feel like you have to.
They also keep the water nicely insulated so that it stays cold longer.
Ok, you've convinced me. I'll get a camelback this month.
I need to get a smaller one. The big one is great because it also holds enough to use as a day pack on hikes but a smaller one would be good for bike riding or even really long jogs now that I am going to be doing those.