When the problem happened to me, first, only some directories had disapeared. Or at leat I couldn't access to them.
Even with a µSd card reader on the PC.
I formated it with the storage tool, on the HD, because the PC would'nt see it.
A week later, I couldn't access to the card anymore. Neither on the HD, nor on the PC.
I concluded that the card was destroyed.
Hopefully it was still under warranty.
I don't blame the cooked ROM I was using. Maybe the SDtuneup with some parameters I entered with Advanced config tool did the mess.
Like power management.
My first SD corruption occured when the card was almost full, and I was downloding a file with Opera. In the meantime I plugged in my PC in mass storage mode. I recognize my error. But instead of simply having a file system corruption, why did it destroyed the card ?
Because after then, the card access was longer. Perhaps the system was trying to recover some bad sectors ? I'm working in phone industry, and we do a lot of tests on these kind of use cases. So I can't beleive HTC hardware isn't that robust.
In my case, it ended with a hardware destruction. Even on other devices (with other OS/ ROM) it also failed reading.
Bad luck with a weak µSD card ?