Yesterday i formated my old windows 7 partition to install windows 8. I had this partition mounted in my fstab using UUID. When my partition was formated the UUID changed as usual. I installed windows 8 and all was OK but when i booted archlinux, systemd couldn't (obviously) mount the windows partition. The problem was that I could not do anything. The boot process stopped, I couldn't change to another tty, only ctrl+alt+supr worked. All I could do was start a Kubuntu livecd, and edit my fstab adding the new windows partition UUID. Was that the only solution?
Excuse my poor English.
I think systemd would have timed out waiting for the device, but the timeout is pretty long. IIRC it's 90 seconds, maybe even more.