Since my account was down, he let me play his account for a bit (which is terrible for account security! Imagine all the money I could have gotten by selling his account on eBay!) and I did a bit of questing as the Warlock. There a few differances between warlocks, and the class that I am most familiar with, the Mage.
Mages die a lot. Warlocks, not so much. Being a Mage is all about distance and controlling the battle. You see, we are a squishy class, unable to withstand being hit in the face with a large weapon before succumbing to grievious wounds. Warlocks however, have handy demonic pets, whose sole purpose is to take a beating while the Warlock burns their foe with unholy magicks.
If, somehow, the Warlock pulls aggro off of his pet, he has several options with a bad guy whaling on him. Fear, Drain Life, Health Stones, heck even their default buff gives them health back. Oh! Oh! And you can't run out of mana! If you're a good warlock this is impossible because you can convert health into mana!
A mage on the other hand, if his frost nova fails and if his blink is on cooldown has one option. Death.
Okay, not really, having played the class for a while now, I have to say that mages have quite a few escape mechanisms that make them quite slippery if played right. It's just that 'Locks have it so much easier :P
So, in honor of the rarely played Warlock It, I present this picture, what I been draw at McDonalds.

And today! She waved at me! What does that meeeean?