Camelbak in the warm months, bottles in the winter.
I used to always carry water bottles when hiking. I discovered the benefits of a Camelbak through mountain biking and now in the warm months, I would never go back to bottles.
Weight: A 100oz bladder is lighter than 2 nalgene bottles, nevermind the 3 bottles (32oz) that you would need to carry the same amount of water. You have to carry a pack anyway, so there is no added weight there. Most new packs are hydration blatter compatible.
Convenience: I find it a lot easier to drink on the go than to have to stop, get my water bottle out, open it, drink, close it, put it back. With the Camelbak I don't have to stop to drink so I drink more and keep myself better hydrated.
As for cleaning it, I have a simple rule: do not ever put anything other than water in the bladder. Putting in Gatoraid or fruit juice will just turn the bladder and the hose into a mold factory. Since I only put water in it, I just run some hot water through it. If the hose looks like it is getting really dirty then I just huck it and get a new hose. They are really cheap.
If you are worried about how much water you have left, just take off your pack and stick your arm down inside and feel how much is left. If you are used to it, you can just stick your arm up between your back and your pack and squish the pack. You should be able to tell how much water is in there.
My warm weather "backpack" is a Camelbak Blowfish. The pack has a 100oz bladder, and stores almost 800ci, which is plenty of room for a gore-tex shell, fleece shirt, hat, polypro glove liners, power bars, some gorp, map, compass, etc. Super lightweight and everything you need for a 10-15 mile dayhike (probably more than you need for some of the real speed deamons on here).
To carry 3 nalgene bottles to get the same 100 oz of water, you would need a "real" pack that has 2 mesh bottle holders on the sides and then clip on the 3rd or put it inside. Most packs that I have seen that have bottle holders on the side are bigger packs, like 2-3000 ci. Just the empty pack probably weighs as much as my camelbak pack, jacket, fleece shirt, hat and gloves, and maybe even some gorp. If you go with a smaller day pack and put the 3 bottles inside, I can just about guarantee that the hard bottles sticking into you back will not be as comfy as the soft squishy bladder on your back with a camelbak.
I do not like the cheap playpus design, so I have only used Camelbak bladders. I have never had any problems with the bladders leaking.
- darren