@Elyx

The problem is, while we have of minor annoyances which are persistent throughout the life of any leveled mage (think blink's spottiness), things really start to get noticable PvE side when you reach T6. Scaling is really bad since warlock's scaling is absolutely OP.

I suspect T6!warlock is beyond Blizzard's comfort zone for a class's OP situation (based on changes upcoming to Wrath, we know they don't like the direction of destro shadow in T6). However, because of the way they designed their raid encounters they can't just bring warlock damage down to something more reasonable now. Thus, they're addressing the situation at the expansion reset.

In Karazhan, you're not going to really see the stark damage component of what's wrong with this class. I guarantee it. So know that going in. You might realize whatever's wrong with mages PvP-side at a more entry-level, but I wouldn't know: I'm no one to give input about mage PvP as I can't stand it, and won't PvP with my mage even to get best-in-slot gear PvE wise. I do my PvPing on my healing priest.

Honestly I don't mean to insult you, but if you truly want to know whether or not a class' perceived situation is real or just QQ, you'd probably get more accurate results just from reading the theorycraft at Elitist Jerks' forum. (I can't do math to save my life, so they're an excellent resource for me especially.) It's really hard to assess the problems of a class in the PvE side of things without having seen more of the class in PvE than Karazhan.

Another example, I'm leveling my feral druid and she's only 46 now. At this point in time, I would say that feral is super OP, but I know from research that bear butt tank itemization is truly crap and you have to arena to get gear in some slots. That's the perception of a feral far higher than my own baby 46, and while I'd say feral is fine, there's a whole other subset of feral in endgame which is not fine. (I don't believe you should be required to PvP to reasonably obtain PvE gear.)

Just goes to show how random factors like level or progression can mean the difference.