Since the introduction of the SuperDrive (officially known as the FDHD for a while), users have had mixed feelings. On the one hand, no one minds having 1.4 megabytes of storage on a single floppy. On the other hand, some people have had troubles with the SuperDrives failing to read certain disks and others have simply been confused about the differences between the SuperDrives and the standard 800K floppy drives.
The SuperDrive requires the SWIM (Super-Wozniak Integrated Machine, by some accounts, though Super is sometimes replaced with Sanders) chip, which limits SuperDrive usage to newer computers. The most confusing model is the SE (and probably the IIx, though I have no experience with them), which had its 800K floppy drives replaced with SuperDrives. So pay attention if you are working with newer SEsthey have little stickers on them to indicate the drive size.
SuperDrive problems stem partly from the weaker magnetic fields that it uses in comparison to the old 800K drives. It is easier to lose a bit here and there with the weaker fields. In addition, the SWIM chip does much more work than the old IWM (Integrated Wozniak Machine) chip because the SuperDrives can read and write all Macintosh and ProDOS formatted disks as well as DOS formatted disks. It seems that the price for this power is an added level of flakiness.
Some people have complained that disks that won't format in a SuperDrive often do format in a PC-compatible drive. This happens because the Mac will not tolerate errors on the disk, while DOS will lock them out. The Mac does so because a disk with an error at formatting will never be predictably reliable, whereas DOS assumes that it can lock out any errors and use the rest of the disk without problems.
Usenet people have suggested ways of avoiding trouble. First, NEVER format a 1.4 megabyte disk (with the extra hole) as an 800K disk, either in the SuperDrive or in a normal 800K drive. When you put a disk into a SuperDrive, the drive looks for an extra hole in the disk. Based on what the drive detects (using an optical sensor), the drive switches into the appropriate mode. The drive's high density mode uses weaker magnetic fields and cannot overwrite the stronger fields on a disk formatted at 800K. Second, if disks are formatted once, but refuse to reformat, try erasing the bad floppies with a bulk tape eraser (or very strong magnet). Bulk tape erasers generate strong magnetic fields that will completely wipe out any data on the disk but may remove some soft errors as well. Third, use good disks. The el-cheapo disks may work fine, but I wouldn't trust my backups to them. I personally stick with labeled Sony disks, which can still be had fairly cheap. Check the ads in the back of MacWEEK.