I started the upgrade last night, before I went to bed. I had to get the beyond the point, where the old packages get removed and they asked me a few questions then. Afterwards it ran through the night.
This morning I had to solve a boot configuration problem, but that was solved easily by letting them suggest a fresh configuration (apparently well based on the "partition logic": "where is what").
After the 1st 'rcxdm start' no window manager was running, but 'env DISPLAY=:0 metacity &' did the job. I have done that for a while now on that box, and I would love to know, how to get rid of that ennoyance.
Well, "devilspie" (aka "Devil's Pie") (for enabling features, that the minimalistic metacity does not support itself -- you missed it? try it!!!) and "gkrellm" where not there at first. Pointing yast to its OSS and non-OSS standard online repositories and installing from there helped in these cases.
To be continued.