I was going through the canon website looking for some info for a friend's 40D and chanced upon a section of info that said that formatting a card is not the same as doing a low-level format. Apparently, format only renames the folder to become invisible not deleted. The picture file is still in the card. Using a low-level format erases the info and "defragment" the card. It also suggested that low-level formats should be done routinely to ensure the card does not slow down.
No lah. All solid state memory does have a fixed number of read/writes before they may start failing, but there's little difference between a format (which just tells the FAT to mark a file as deleted) or writing a pic.
And even so, this MTBF is usually between 10-20,000. So even if you format every day, it may take 10-30 years...