Boot any OS on Earth from a CF card or Microdrive
 

BOOTING FROM FLASH is nice, that is, if your system's BIOS specifically supports booting from "USB Mass Storage" devices. I found the hard way that plenty of systems do not. And then there's the issue of the limited R/W life of flash memory, making flash devices unsuitable to place an OS's swap file or even temp files on it, thus making real "spinning drives" much more appropriate for the job.