I switched cards with my Hero's 8GB and it seems fine EXCEPT that maybe once a day or so, the card starts running slow (checked by SD Card Speed Test app). A reboot fixes the speed. Makes me wonder if I don't reboot if it will eventually start failing again.
Interestingly enough, I have had issues with uploading images to Picasa where the images show up on Picasa with some corruption (jaggy grey bar at the bottom). Seems to only happen when the card is in the funky slow state. A reboot and reupload fixes it.
Now HERE'S where it gets even MORE interesting...the same thing is happening on my Hero! And I've updated my Hero to 2.1 and it has Sense on it as well.
I'm not saying these issues are necessarily related, but it's simply more data to figure out what may be wrong. Personally, I think it's a 2.1 software bug, probably with Sense.
Would be interested to see if anyone else sees what I am seeing...a slowdown of the SD card throughout the day. Basically, run SD Card Speed Test throughout the day and note down the numbers. For me, by the end of the day, it has a write speed of 1mb/s, and that's when I get Picasa upload issues.