I"ve been using a Camelbak Unbottle (3L) in an Osprey pack whenever I go on outdoor video shoots. I find it helps me keep up my pace when I'm shooting outside all day in 90 degree+ weather. I usually fill it up with ice, then water and that keeps me going for a full day. I think the part that helps me the most is the fact that I'm constantly taking sips throughout the day. I have to keep on reminding the rest of the crew to drink water instead of passing out.
I also use a Nalgene pack with 1.5L bladder, but I go through that too fast.
I just bought a Camelbak BFM, which is a 'military' camelbak. As acwire mentioned, the main difference between civvy and military camelbaks as far as I can tell are the materials used. The military camelbaks are significantly heavier. The BFM is over 5lbs empty! With the current trend towards Ultralight backpacking, it makes sense for them to differentiate the lines. The military Camelbaks also have drain hole grommets which I haven't seen on civilian camelbaks.
Theoretically, the heavier materials used should last longer, but in my experience, construction details such as stitching methods and quality play a bigger part in longevity.
I usually rinse out the bladder and hose with a little dish soap and water, After extended use, I'll scrub it out with the brush, rinse, then let it stand with about 1L of water and baby bottle sterilising tabs, then dry.
Nope, haven't had a leak yet.