A wee while ago I searched for information on the new Demonology talent Metamorphosis, and found very very little on the subject, so having tested it out I wanted to share my newfound knowledge:

This talent is amazing! As two level 67 warlocks in quest/tailoring greens I was jumped by a feral druid wearing a few pieces from each of the first three arena seasons and I obliterated him!

As a multiboxer, most of the demon abilities are not that exciting. I haven't tested out the demon charge on mobs or NPCs but on target dummies it seemed bugged, the melee cleave is awkward and seems futile without any melee stats, and if you're that far into Demonology you should have a pet to tank, rendering the taunt VERY situational.

But the shapeshift itself is a considerable boost to your damage, the armor increase helps fend off melee foes for that little bit longer, and here's the part that matters, Immolation Aura! See http://www.wowhead.com/?spell=50589 for specifics.

451 Fire damage per second for fifteen seconds works out to 6765. (Of course that's the base damage, there's still spell power, and the demon form to boost this and of course resilience and resistance to reduce it) Multiply that by however many warlocks you have, because they all stack.

In PVE or PVP it's a beautiful panic button. I've had some close calls, but thus far it has saved me every time.

Throw +damage trinket, Metamorphosis, Demonic Empowerment, and Immolation Aura together in one tidy macro and the result is utterly rapacious.

Do it, you won't regret it (and once you're a few levels into Northrend you can get back Imp Life Tap and Soul Siphon).

Oh, and I should have mentioned, it looks pretty cool.

Edit: My comments on the cleave spell aren't entirely accurate. It does use spell damage instead of melee stats, I still found it quite underwhelming though.