Quoted from the forums:

I took adventage of the new lvl 50 char gift and I made a Demonologist. I loaded in Khemi, and I quickly went through my "Friendly" spell list, clicking on all of them just to see what happens, I got some buffs which I really didn't know or care what they do. I tried some spells that were already automatically placed on my hotbar but most needed a target, so I made my way to Eighlopean Mountains to test it out.

You want to read it all ...

First spell that I checked out was Shockstrike, then some AoEs. Then I run onto lvl 52 Dark Templar, and we started fighting. As soon as the fight started somebody was ringing a bell at my door, so I had to get up and go AFK.

Now here is the kicker, I have a macro setup to execute the same button (spell) every 0.5 secs forever. So before I got up, I executed that macro, and the spell that was on that macro just happened to be Shockstrike. I came back about 30 seconds later, lvl 52 DT was dead and I'm standing there (lvl 50) with 60% HP. I KILLED THE GUY WHILE I WAS AFK! This is on top of the fact that I did NOT have any feats at all, I completely forgot to use my feat points before I came to the zone. Combine that with the fact that I don't know anything about my class (as I was logged in for less than 5 minutes) and then you get a fugly picture of the imbalance between the DT and Demonologist. That's just one example.