count me in on this.... most of desktop RPi's boot from SSD, another one boots from HDD, and another one boots from USB thumbdrive...
ok lets take it up a notch...
booted my RPi2Bv1.2 on old samsung 2.5" 250GB HDD! (no microSD card on slot). Just set the OTP bit!
used as a desktop with attached to 7" monitor, keyboard and mouse, LAN connection
Worked fine, used it for about half a year.... coding and stuff, some chromium browsing.... mostly used for maintaining other SBCs via ssh....
its now working as a NAS though...