I have LOTS of problems with my 1G MMC. Even with sync enabled (kills speed), if I untar a large file (IE, debian chroot tar), it will error and eventually 'eject' the card (That is, I can't see the mount anymore till I restart).
If people are using SD's without this error (and dare I say, at async), then I might toss this and get another better brand.
A work around, is to run the following in another terminal whilst doing big file operations: -
while [1]; do sync; sleep 5; done
Just Ctrl-Break out of it when you're done.
- Bundabrg