I've had a few camelbaks, both big and small, and I must say this is my favorite. I've also had a couple of other hydration packs, TNF, etc., but this one is my favorite (sounds like I go through a lot of packs, but I have 5 brothers and they get the ones I've slightly used). Every once in a while I run in the ditch on the side of the road 15 miles to the starbucks closest to my house, and this pack is perfect for it. It serves best for any day length or less off road activity (where light and fast is your ultimate end). Pack some zone bars, fruit, water, bike tools, and a rain jacket, and your set to go. If you are going to do something longer than a days length where more clothes might be needed or different layers, I would suggest getting the larger octane.

I would give this pack a 3.5 if possible. Pretty decent overall backpack, priced right I would say considering the bladder is included. Decent weight, very comfortable, good amount of storage space considering how small it packs down when the middle is zipped up. Not the most durable pack. Bought last Christmas and mine is starting to fray fairly bad in a few areas and won't last another year. My biggest complaint is the back panel's so called "air director". I've worn this thing quite a bit in Utah, and any temperature over 85 degrees and my back will be soaked with sweat. I rarely sweat otherwise. It does not breathe at ALL. No exaggeration, my burton pack made for snowboarding, with insulated back panels, is MUCH MUCH more breathable than this thing.
Overall I would say this is a pretty good pack. If you can get it for $60 or less I would say buy it. Avoid this thing at any cost if you hike/use in any temperature above 85 degrees.

The Octane 8+ is perfect for running and biking. When I'm running in the mountains it stays close to my back and it really is comfortable to run with. You just have to, as mike.mull is saying, get the straps adjusted correctly. When i'm on my bike, whether on the mountains or the road, it works perfectly well. It is not a "big" camelback, and it's almost aerodynamically designed, which is a positive thing when you are out on your bike.
It also has a lot of storage place, I must say I'm a big fan of the expansion system. The only negative thing is that the drinking tube (not the bite valve, the tube that comes out of the hydration pack) is bouncing on the lumbar regions. I use to just turn the whole hydration pack around..

Okay, so now I've used this pack for about everything. Biking, skiing, climbing, hiking, trail running and the list can go on and on and on. It's been great for everything! It's really pretty light alone so running with it was no problem. It's comfy enough that biking/hiking was no problem at all. There are enough compartments and expansion that you can fit plenty of gear inside. This was definitely a good find and well worth the dough!

I wore this pack for the Trans-Rockies run (6 days, 106 miles). I was happy with the available space for clothes and gear, the hydration reservoir was adequate, and it's surprisingly comfortable to run with. If you are doing long runs (3+ hours), it's very important to get the straps adjusted correctly. One side too tight or loose will result in chafing at the shoulder straps. Adjusting the drinking tube is tricky also-- the normal arrangement leaves the bite valve bouncing off your sternum.

I bought this pack based on the good reviews posted here. The pack itself has good volume and is layed out pretty well overall. The quality is an issue however. The shoulder straps are sewn to 2" webbing with the stiching going only thru the top foam layer of the shoulder strap, not thru the entire strap. Both shoulder straps are tearing away from the stitching after 2 short day hikes. I've since returned this item for a refund. The stitching should go thru the entire strap for strength as these straps bear much of the pack load. Since many of the camelbak packs are sew this way i would not recommend their packs.

LOTS of storage space. Fits comfortably while active and doesn't slide around. The only thing I would change would be to have a larger reservoir. I think the they advertise that the bladder should last from 1-2 hours of active use. I'm lucky if I get 45 minutes.

I wanted a sturdy waist belt to get the weight off my shoulders. this does the job, but the shoulder straps are skinny compared to my old 'chaos' .holds plenty of water and gear for my trail rides. I plan to keep it best camelback so far.