Just had some great success myself, started looking last night for the minfernal and logged in this morning to 3 of them sitting in front of me with no one else in sight. Grabbed 2 for myself and held one in a battle till i managed to get one of my wifes alts there to cage it.
Best way to get this guy i figure is to make a DK alt on a low pop server / battle group, and check the spawn first thing in the morning. My home server (sisters of elune/cenarion circle) is super low pop, as are most of the other realms it crossrealms with, so that might be a good place to start if you want to stick to a US realm. Its on west coast time, so if you live on the east coast you have a serious advantage in the mornings. Also have no problems finding other rare spawns like valks and whatnot.
Sorry didn't mean to hijack the original topic, just still excited about pulling 3 of them this morning.
I'm on alliance side on SOE/CC, if anyone needs any help or anything. sonicfear#1555