I also have the Dream. It's a great size for most rides, holding 2 liters of water and a snack or two. I don't feel at all encumbered by the weight, and I only sweat under it on really hot &/or humid days.

I did decide, though, that I wanted more compartment space so I picked up one of the new Chaos models. It's a cool golden brown color, which I way prefer to the usual Camelbak shades (a great big thank you to you mtb'ers out there who convinced Camelbak to go earthy ). It's a men's model, though, so the straps are a tad wide and the length of the pack might be a bit long. I have yet to actually use it, but I'm thinking that being able to carry my camera and stow cold-weather gear will make up for the not-quite-right fit.