While you can't solder it in tight quarters, you can certainly use soft copper lines rather than rigid. Sure, its tough to bend, hard to keep from kinking (in tight bends), and more expensive, but not as much soldering. They do make tools that prevent kinking (they look like wire wrapped around a tube; refeerenced in that article) that help somewhat; lots of heat helps too. Also, you can choose to insulate the 'cold' lines very easily. The good thing about the tubing is that you can make it so that the entire loop is at least 1/2" ID (or whatever ID you choose), since the fittings are made to fit around the tubing.
Basicly, its a better performer than tubing, but like all things that are 'better', require more time to make & setup. It also takes a bit of skill & luck to get things right. The last thing is that you can do some crazier stuff with all copper rather than tubing, since its easier to chop & fuse copper parts than chopping & fusing (must be melted juuust right) PVC tubing.