I've installed woody from potato via dist-upgrade "apt-get --fix-broken --show-upgraded dist-upgrade" now three times in the past year; twice on my own machine and twice on others, and have allways been successful. The first time, dpkg couldn't preconfigure and I had to start installing packages one by one with apt-get until I finally found out the complaint was that I didn't have apt-utils (if I remember correctly); after I installed that, everything was fine. I think one other time I had to run dist-upgrade to get everything to download and install, but that was no big problem. A lot of the trick with upgrading to woody from potato is making sure everything downloads. The two things that can prevent this that I can think of immediately are: a ppp connection that broke off--but you should know about this because you'll get messages; and either not having the right lines in your sources.list or, if your potato lines are still there too, not having the woody lines in the right place, above the potato lines. Of course, I know it's not that simple; there are plenty of other things that can go wrong, but these were the ones that I found. At any rate, I'd be pretty comfortable now upgrading from potato to woody if I had to do it on a machine of my own or for somebody else.
-- Cheryl