MPEG Streamclip (assuming you have the Apple Quicktime MPEG 2 component) can let you cut the VOBs into bits and rejoin them into an MPEG file which you can then burn to DVD (I use Toast, I assume iDVD can handle it).
It's fast and there's no recompression involved at all. Everything is just rewrapped and joined.
Negatives: the only editing you can do is cuts and MPEG Streamclip cuts only on keyframes, you can't cut on just any frame.