I hate having stuff on my back so much that I just bought this Showers Pass Veleau 42 bike-mounted hydration system (only $29 at MEC in Canada!). Only rode it once, and felt so FREE having nothing on my back. Noticed the lid of the hydration system if I was sitting back in the saddle, but it didn't bother me. As the reviews have all said, the "gravity kit" (the magnet strapped with an o-ring to the top tube) came off on my first ride. It does not stand up well to me dismounting and standing over the top tube while waiting at lights. Fortunately (or maybe it doesn't matter) I saw it hanging there at a light and was able to pocket it. That said though, I'll just be somehow mounting a magnet or even a small piece of steel with zap straps to my top tube for a more permanent receiver for the magnetic mid-way along the tube.

Pretty sweet And nothing left to wear on my back!