I have about 4 TB of media spread across 6 drives. All of this is backed up to another set of external and network drives. Because I frequently run auto-import as well as my backup program which scans for changes I have developed a good sense of how reliable hard drives and/or Windows are. My experience has been that about once every 2 months I see one or two random files (out of 193,000) change. Usually the change is a single character in the file name. I have no idea what causes this. Usually a reboot cleans up the problem but sometimes it does not and I have to restore the file from the backup.
The lesson is that you cannot trust that your media is safe just because you are not getting any drive error messages from Windows. You need to check the data every once in a while and MC's auto-import is one great way of doing this.
Never, ever seen anything like that. I've got well over 4.5TB of stuff (Approx 225,000 files imported into MC last time I bothered to check, this spans 14 drives of various ages & sizes), which has collected over the past 7 years or so.
One of the drives in my server is the 20gb original from a Windows 98 box, and everything is still precisely where I left it.
For that matter, the only drives I've ever had die (2x Samsung 400gb Spinpoints) were sickly from the start, and they never had any important data on them
My personal approach on this front is to use any new drive as the general download/ data dump. The drive that it replaces then moves into the main storage pool after having been running constantly for 6 months or so, which gives enough time for any imminent failures to become apparent.
Admittedly, my main PC and the network clients are the only people accessing this data, so there's no real external error factor involved, which is present in your setup.
Even with this in mind, if you're having filenames randomly change then TBQH you have hardware issues somewhere. I'm not going to speculate on what these might be, but something is up.
Cheers
-Leezer-