Thanks. When things are complex people often treat it as magic. I was trying to prevent people to learn rituals that (in my opinion) do not help at all but make things yet more confusing.

As for completely dead cards the real reason why it happens is currently unknown so we can have only bold (and most probably wrong) theories. From user reports it looks to me like it may (or may not) be related to

- using card in external slot; bold theory is that the slot is capable of more fine grained voltage control so card in that slot runs at different/lower voltage than in internal one so maybe some cards don't like it sometimes, but maybe the simpler explanation is that people remove cards from external slot more often so the chance of corruption is higher

- copying/downloading data from network directly to the card (using maemo mapper to download maps, downloading big files via wget or scp), bold theory is that (especially long lasting) wi-fi transfer may produce high power drain and (with the combination of lower voltage in external slot) may cause the card to be momentarily 'underpowered' when doing the write operation and fail

So because I don't understand it too, my rituals would be
- avoid using external slot and prefer the internal one
- avoid doing long lasting data transfers from wi-fi to card

But I admit I may be completely wrong so in fact you may learn rituals that do not help at all but make things yet more confusing :-)