Most services are running, and I can ssh to it without problems. Just have no local consoles (cannot CTRL+ALT+F1,F2...) and no graphic session either....
Looks like somethings not playing nice with the new kernel, but, how do I trace it?
Answering myself (as recommended ;-) ):
The nvidia drivers must be rebuilt after kernel upgrade (and BTW, dahdi drivers also).
I got local console access sending some CTRL+ALT+F1 BEFORE the nvidia driver was actually loaded into the kernel. That way I learnt it was some misbehaviour of the driver preventing me from falling back to consoles later.