I made a new thread for this topic, as I felt a similar one veered off course. I just wanted to share that it IS possible to use HD 3.5" floppy disks with standard Apple II hardware, using the 800k disk drives. I do this on Apple //e's and Apple //c+'s all the time and I really never have a problem. Apparently there is an issue if you try to format these (typically pre-formatted with IBM DOS format disks), due to the preloaded format.
Here's my technique; Just take a good magnet to these disks, and rub it all over the outer housing. You have now removed the pre-existing format. Slip it into your disk drive and treat it like a SD 800k floppy disk. I format with the Apple issued ProDOS8 System Disk. I never understood why other people haven't done this and keep spreading the meme that you can't use these disks. Sheesh people! They are made out of the same magnetic-ferro-imbedded plastic stuff as a 5.25" disk, just with a finer grain density.