Well, an aftermath of my problems with rebooting.

In braces the reproducibility
1. Sometimes (2/10) the hildon desktop mixes the orientation, staying in portrait resolution. The layout is rotated, though. killall hildon-desktop helps
2. Once: image-viewer takes > 20% CPU, so does hildon-desktop. device sluggish. killall hildon-desktop helps
3. (100%) a particular image causes the device to crash (reboot) when zooming in. Once even switching the photo caused a reboot
4. During mass storage mode, the device exits the mode and freezes, not reacting to the power key. (once)

Does it sound like fs corruption? Or may it be something else. Will fsck suffice or should I rather do a complete reflash?

/edit: tbh, I never did a fsck on my phone. Is there any way of doing a rootfs fsck on phone than using some rescueOS?