Again, a simple experiment was enough to destroy my /optfs... and I was running power-kernel-46 at stock voltages and frequencies. I only tried to activate smartreflex while the n900 was stable, sync had been freshly executed, no apps apart from qcpufrequency and xterm were open.
Crash.
Reboot... opt filesystem borked. Two hours lost in restoring from backupmenu (of course backup wasn't going to work as expected - but at least I did it).

It's my fourth year with Maemo. I'm starting to be tired of it all. I hear the song of Android sirens... they sing of using it, not hacking it, and rest in peace...