I've never even seen the little guys spawn.
As much as I desperately want one (and as a warlock feel indignantly entitled to one) I'm glad collection isn't easy for all of the pets (restless shadeling, anyone?) - so basically these guys show up at server reset only?
What I love are having specific conditions on pet spawns - weather, time of day, it would even be great to integrate mob kills to spawn their little babies that you can steal.
Yes, as a fellow Warlock I have a feeling we won't be able to raise our heads against the Frost and Arcane Mages with their Kirin Tor Familiars until we have one of the MInfernal.