Damocles is right, ulf. That is basically what we do (there's little bit more to it, but not much). The real problem is, as you might have guessed, that for a big level you need a huge number of nodes - especially for the outside levels (3-4 per single tree for example) that need to be placed manualy. I tested some ways to make this process semi-automatic and use less nodes. Although some of the results were quite promising, I didn't have enough time to make it work truly reliable.

EDIT: as for the short zig-zag turns: no one says that you have to turn immediately (flip) all the way to the next node once you've reached the previous one. You could simply go on and start turning the player. For this however you need to be sure that there is always enough space for him to make the full turn (it has to be rather fast anyway) or, which is the best way, check it if it is possible at all and if not, turn him immediately in the direction of the next node.