This is for any mages (and rogues/hunters too I suppose) who also have engineering.
Basically we were on the last boss of Heroic Durnholde, our priest goes down at the end of the last wave, *bamf* I pop invisibility, wait it out, and after 5 seconds use the Goblin Jumper Cables XL on the priest when I come out. She's back and we continue as normal and win. Imaginative use of game mechanics? I suppose it's because we're both out of combat, it seems to work fine.
This in essence gives mages a combat rez, which obviously only works as long you have no dots on you and avoid periodic/boss damage.
I don't know of any other interesting mage-specific uses of engineering items, except maybe being able to "port" to Gadgetzan and having two farmyard animals not one (Gnomish Poultryzer).