The bulk of my names are with Enom and other than a few hiccups recently when they were doing some work on their database I have never experienced any problems. Even then the problems were only of access and availability checks, nothing that affected my names.
Domain hijacks occur but I don't think Enom is any more vulnerable than any other registrar and recent instances quoted on this Board of names allegedly stolen and being returned to alleged owners by Enom are "out of the ordinary" occurrences.