I have been eyeballing this thing for months, wanting to try it out. On my way out of town for the calico 50k I stopped at a local running store to pick up some body glide. While there I saw they had these packs and impulsively bought one. I wasn't so sure that testing out new gear on a such a big race was such a good idea, but I decided to run with it anyways. Man is it comfortable. I only ever filled it to 30 oz cause there were enough aid stations that I didn't need to lug around the full amount. 30 oz didn't really feel like anything. Barely bounced at all, though I like to think that i have a pretty smooth stride. The best thing about it is all the pockets and the drawstring. Midway through the race I took off my shirt, it was nice to cinch it down to my pack instead of tying it around my waist or holding it. Also the pockets in the front are amazing. I was able to put my phone (it is my music and camera) in one pocket and some treats in the other. Very easy to get to stuff when it's on the front. I will deffinately be wearing this for all my longer runs and for any long race where there is not an aid station every couple miles.