Hi Helge et al,
I have tried this Debian 8.0 installation on a spare HD in my C3700. The installer is painless & "runs like a Swiss watch". I had no trouble installing a KDE desktop environment and booting it. The software repository and the packages downloaded gave no trouble at all. The base OS has been rock solid. I have installed boinc/seti@home and that has had the box at 100% CPU load all night without trouble. Some packages have been a bit slow/clunky but given the age of the C3700 that is no surprise.
The only package to consistently crash was "system settings" any time I tried to change display settings. The base OS has not crashed AT ALL.
Cheers, Geoff.