I am training for a 50 mile ultra and so far this little pack has worked great! Perfect amount of water for long runs (20milesish). I have a 28 inch waist and the pack only has about a inch and a half on each side of tightening room and when the bladder is empty its almost maxed out. nice storage on the waist band, each pocket can hold two power gels. The two pockets on the back can hold 5-6 power gels. The elastic band is super nice on the back. I keep a light jacket in there and on super long runs (25+) i have a water bottle that i strap in. Pack doesn't bounce or slosh whatsoever and is super comfortable.

used on my short length runs, works perfect, very comfortable, holds just enough water for a less than 5 mile run, says .8L, you can (technically) throw almost 1.0L in it, it'll fit, barely, has pockets for my hammer gel and keys, little more capacity and it would be perfect, but extremely versitile and lightweight easy to maintain and comfortable

No need to change a great thing, I've been using the CamelBak Alterra since 2006. It's my personal water buddy.

Positives -
Comfortable
Convenient
No flip flopping
Side storage for gels or map
Can put a t-shirt in the back straps

Negatives -
Only 28oz res
It's hard to add more water on the fly

This pack is just right for me! It's small, but wears comfortably and doesn't move or ride up much. I like that it has two small pockets for treats, keys, or a small cell phone. It isn't the easiest thing to put on when it is full because the buckle closer is way over on the hip, but for that reason it won't dig into your stomach when you're running. The one big downside I have with this pack is it isn't easy to fill it to the top and then close it without water gurgling out all over the pack. So far I can't figure out how to remove the bladder from the pack to clean it either. Otherwise, I would recommend this pack for short runs or for sipping in between aid stations.

I hate getting dehydrated on longer runs and I hate carrying a water bottle. I tried a traditional hydration pack that goes over your shoulders and couldn't stand the bouncing. This is perfect. It doesn't bounce and it carries just the right amount of water to last me about 1-2 hours on the trail. If I try to wear this on my hips, then it does bounce a bit as it tries to migrate to the most slender part of my torso. I find it best to just place it a bit higher and then it stays put really well.

I've only had mine for a short time but I did not notice a plastic taste at all. Maybe they've fixed that since March of 2007.

So far I LOVE it. And the weird buckle placement is so that it doesn't dig into your stomach. The front strap is nice and padded and with tiny little compartments for storage.

I have been using it for running and really like that it doesn't flop around, is soft and padded so it doesn't chafe or build up heat. This past weekend I used it on a Competitve Trail Ride and it was perfect! Snug enough not to hit the back of the saddle, and does not throw you off balance like a backpack model, or interfere with rider vests. Pretty easy to refill at water stops, too.