Thank you all for the ideas.
@MaxK1 - This is what I thought as well, running from USB would not solve the issue, although in some places this is sold as a cure for corruption. It may have worked better for some. I would keep the backups warm
. I have also no doubt it's tricky running from flash. "Even files in a different, un-mounted partition..." Well, this is scary!
@jamesh - The card is a 8GB Sandisk class 6, about 6 months old. Worked for a number of months in my first Pi then corruption (after abrupt power down). After fsck it booted again (amazing, huh!) and ran for another month. Then the Pi itself died. Maybe because I plugged the vaccum cleaner in the same socket? Didn't die that day, a few days after.
Got another Pi, put the September Raspbian, all updates, some somewhat heavy activities (compiled node.js from source, installed boost-dev, etc). And then some other heavy disk activity: time-lapse photography, more than 2000 pictures! After a week the card got corrupted. That may have been too much stress if Max is right!?
And 2M Pis ok, just a few bad apples? I think a poll would be required - from the ones that actively use the Pi.
But James, if you are a lucky one and no corruption at all, could you please let me know what power supply and sd card you use (Amazon links)?
So the culprits may be time-lapse photography, node.js, boost and a vacuum cleaner
@gkreidl - I'd move to an USB but it negates some of the reasons to use the Pi - use powered USB hub. But this is what I may end up with eventually. Fine at home, but when I bring the gear to work for time-lapse photography I'd like a minimal setup.
Last thing: the Pi would not boot from the card after restoring with dd from 2 backup! Any ideas here other than throw the card and get a new one? Would dd insist on writing over bad sectors or are the bad ones are marked up and dd transparently uses the new good ones? But you see the problem: getting into too much details about sd cards - ideally one would do real work/play on the Pi instead of learning about sd cards, however interesting those may be.
Eager to follow the activity on making the Pi more bullet proof. Hoping to hear some good news eventually. Merry Christmas!