Thorsten and all, the issue isn't reproducible in snv111/ohac any more either.
Again, I am not aware to have changed anything significant, so for my own peace of mind I will accredit these issues to some Xen-spcific effect (note: I'm running s10 as HVM domUs and snv as PV domUs). I had experienced a total domU hang this afternoon, after which I booted the dom0 - and from this point on all problems vanished. Thank you very much again for your help and advise! This is fantastic! Nils