I rode the Rush at Pontiac Lake this afternoon, a trail that is fairly rough in spots with rocks, roots, and fast downhills with braking bumps at the bottoms. There is a preferred line in most sections, clearly defined by its smoother surface as it winds around some of the obstacles. I found that I was starting to ignore the established lines and instead would be pointing the bike straight over the rougher sections. The only thing I didn't like was all the chain slap noise but I installed a Lizard Skin on the chain stay tonight so it should be quieter now.
I tried out the Wingnut and it hardly felt like I had anything on my back. I liked the side pockets that I could reach while riding. I had an email from the company today after I questioned the bite valve. It turns out that it has an on/off function and you pull the valve out to turn it on. When I tried it yesterday it was barely on which explained the trouble I had getting water to flow. I pulled it all the way out today and it works much better. It seems rather large when it's in your mouth but it works. I think that Camelbak still has the best valves.