I don't do much hiking in areas where fires are permitted, but I have played with a pocket chainsaw before. They do work fine, and you can work your way through large logs.

For most planned situations, though, I'd rather spend time hunting for smaller downed branches and use something small like the Opinel Saw knife, or just carry my big leatherman.

http://www.amazon.com/Opinel-inch-Beechwood-Handle-Folding/dp/B000REZBW6

I haven't used a sven saw, but would rule it out based on weight.