I have to admit that I use hd floppies on my amiga 500. Is it okay to do? Some people say no others say yes. I have had no major problems so far.
I found them quite unreliable at times, but generally they worked OK. May have just been cheap quality disks though.
I also used to use DD floppies formatted as HD in the Acorn RiscPCs, never had a problem with them either (RISC OS didn't care whether the HD hole was present or not IIRC).
Chris