SD card Issues...normal?

I have a couple of SanDisk 1GB cards I bought to use for Wii backups and now Homebrew.

Yesterday I decided to try installing SDLMAME on the homebrew card; when I tried mounting it on my iBook using my USB iApp card reader nothing happened. At first I thought either the recent security patch I installed had made the OS X USB drivers incompatible with it, but it wouldn't work on my work Windows laptop either.

I then tried putting it back in the Wii, but the Homebrew Channel didn't show it either, so I guess my card got corrupted by the reader? Seems a bit odd, frankly and it has only been a week since I tried running any Homebrew apps. I even tried viewing it in the memory management screen on the Wii thinking I could reformat it, but it just said that this card wasn't usable by the Wii.

Another odd thing that's happened is that my save backup card no longer mounts on my iBook. It tries to mount it, but says the card isn't compatible and offers to format it. I can still view the saves in the Wii and copy back-and-forth, but if it's FAT16 or whatever, I don't understand how the data structure could no longer be viewable.

Ideas? I would have thought SanDisk the most reliable brand, but basically I have one dead card and one that could be on the ropes. I don't do a lot of read-write activity to them, but just in case my new 256MB homebrew card now has the lock on it.

I did delete all my Channel backups from the save backup card because it's faster for me to re-download than copy from SD and because they're not cross-system compatible anyway -- could that have corrupted the filesystem from a computer p.o.v?