I've been multiboxing 4 warlocks and a priest up to 70 where I already had some characters ready to throw into the mix (mage, warrior, paladin, druid) to set up a "proper" pve team.

I've done several instances with 4 warlocks and a priest so far and found it pretty manageable and fun. I went into mana-tombs in heroic mode just to see the difference and wiped twice just clearing the first three pulls in. Granted, my guys have trash gear - but considering how little my gear affects my demons I realized I will have to get a real tank.

So last night I got my protection warrior all set up, modified a few macros for my slaves to target off of him and I was set to go. I went through Shadow Labs in normal mode to get a feel for it and it was pretty rough going.

Here's the troubles I ran into:
  1. I had to worry a lot more about placement, letting my tank run ahead. Previously this was a non-issue.
  2. I would forget to take my guys off follow, leading them all right into melee range to be cleaved.
  3. I would get so focused on my tank getting heals that I'd look up and notice nobody is dpsing.
  4. I would be so focused on dpsing that my tank wouldn't get enough heals.
  5. Num lock would be turned off, which meant no heals for my tank since my heals are bound to my number keys (I'm no longer in range to hear the heals going off, which was very helpful in my previous group composition) -- this wiped me twice.
  6. I noticed a large drop in dps due to that 4th dpser not being there. He happens to be the best geared . (Additionally, that one warlock I'm missing already has 375 alchemy and herbalism.)
I'm going to keep trying this, but I've got to say moving from 2 classes to 3 has added a whole new level of complexity. Unless someone can confirm that a 4 warlock 1 priest team can do heroics in wotlk I think this is the only way I can really proceed. My plan was to be able to do heroics.