[Galaxy Note II General] Snakeforhire:
It is the SDcard, no doubt about it. Some say that it's the reformatting from exFAT to FAT32 which is causing more stress on the internal disk controller, but somehow I doubt it. Since an SDCard is designed to emulate the working of a HDD (internally and from a logical standpoint), I doubt that putting a filesystem that is older on it would do much difference as far as it's concerned, it just distributes the bits about the endless rows and columns of capacitors, sends a TRIM command whenever there's been bits deleted to reinitialize the whole 8bit block that contained them, spreads the new data to a new "fresh" location and voilà, the way they're organized in the cells isn't much of it's concern and as far as wear-levelling is concerned, FAT or exFAT shouldn't make much of a difference). If anything else, it's the exFAT which should be spozed to put more stress over it since it's designed to be much more intricate and to incorporate (some of) the benefits of journaled FS's.

That being said, I'm only a rookie at kernel coding, and while my knowledge of flash memory technology is starting to be quite consequent, the "inner workings of exFAT and the more or less strains it puts on block devices vs. FAT32" binder is still sitting on my desk waiting for me to find a chance to read it.. ^^

I think the problem lies more in the voltages that Samsung devices use to power those SDCards, maybe it's too flaky or inconsistent for the card and cuts a good chunk away from its life expectancy, and makes the controller die prematurely, I couldn't tell... But if I had to bet my money on aprobable culprit I'd look towards the memory controller..

The card being not recognized at all or seeming completely blank sure points towards this probable cause of failure. Controllers have always been 'the weakest link' in flash memory technology, they actually have a far lower life expectancy than the memory cells themselves (about 1000x or so), so the cells almost never even reach the end of their theoretical lifespan before the controller croaks, rendering them totally unusable because it's too expensive to put redundant controllers in a single chip (rightly so, since the backup -having the same MTBF and most probably coming from the same batch as the primary- would certainly die shortly afterwards.. However, it might be awfully nice in order to get your precious data back before the inevitable happens)). So when you hear that flash memory only can withstand about 10000 write cycles nowadays, they're actually talking about the memory controller and not the chips/cells themselves -or they're just dumbly repeating what they've heard about just to look "hip", and such ^^),

All I know is that I had 2 pieces of the red CLass10 64Gb, one which croaked quite quick in my SGS2 (less than 3 months, it's still sitting in my toolbag with the spare ones waiting for me to find time to organize an RMA), and an exact same which has seen some months of service in the i9100 and for the past 6months+ in my N7100 : so far so good for this one...

I also have two 32Gb (black, one class6 and another class10 I think), but these seem immune to this plague as they're 1yr+ by now and nothing to declare..

On the other hand, I've had 4 Samsung 32Gb class10 : one died in less than 3 months, and among the 3 survivors (all are choked full o' data, less 'n 500 Mb available on any one of them), one is showing abnormally slow transfer rates for some months now, and it seems to make the mediascanner of my i9100 "go crazy" all the time (meaning it's looping around scanning the same file over and over again, killing my battery veeeeery fast.. But neither fsck.msdos from busybox of chkdsk from windows7 can't seem to pinpoint the culprit.. :s), so whether it's only happening to sandisk is doubtful..

When you reach such amounts of data density over such a tiny surface that is constantly exposed to the elements in the air, temperature and humidity, various shocks (even tiny ones. remember the edges of most sdcard slots are sharp metal ones), and not necessarily caring hands and so on, a tiny scratch or dent is very quickly put into such a fragile device, and a tiny scratch is all it takes to rupture one or more inner circuits, and then "there goes the weekend, and your 50$+ gadget"... :/