7. My biggest mistake: not requiring vent.
Nihilum used to be famous for raiding without vent (and for all I know Ensidia still doesn't use it). Your PuG is not Nihilum, and it's a giant pain in the ass to have to explain things over vent and in raid. I am nonetheless very sympathetic to people who don't use vent and/or don't want to download it, because I was in their shoes when I started raiding, but there is no text-based substitute for the speed and clarity with which you can explain a fight and answer questions.
If you absolutely do not want to use something like Ventrilo or TeamSpeak, I'm OK with it as long as you know the fights and employ a modicum of common sense. If you absolutely do not want to use it and you don't know the fights, I can't justify taking you over someone who does.
8. An entirely non-PC (and, I admit, possibly incorrect) observation: pugged DK quality is a total crapshoot, but the quality of the average Rogue, Mage, Warlock, and Hunter has gone up.
I have a pet theory concerning the vacillating population numbers we've seen in classes since Wrath hit, and the observation is borne out so far through my experience in hundreds of PuG's (yours, of course, may differ, and I'd like to hear if they do).
If Zardoz's numbers are within shouting distance of accuracy, we can reasonably expect that the vast majority of Death Knights being played as mains at 80 are rerolls from a pure DPS class. Some of them, like the Death Knight main tank we had the first night of the run, are extremely good. Some of them, like one of the DK off-tanks we pugged, need some help. But it's my theory that the players who didn't reroll from a pure DPS class entering Wrath are more likely to be the people who played their class well and are emotionally invested in the toon. It has become much more uncommon for me to run across an inexperienced pure DPS class since starting Wrath. For all I know, this is a demographic reality (if it is indeed reality) unique to my server, but Zardoz's numbers seem to provide a little insight into how this might have occurred. Your mileage, as they say, may vary.
And the big one:
9. Almost anyone can learn to play their toon effectively in a raid, but you can't teach a jerk not to be a jerk.
I don't regret telling people that great gear wasn't necessary to come, and I consider it a point of pride that we had two players with little to no Naxx experience regularly land among the top 5 DPS after listening to peoples' fight explanations and asking questions when something didn't make sense. "Skill > gear" is a saying that gets trotted out a lot, but I'd also argue that "Nice" and/or "Sensible" > gear. Almost anyone can learn how to maximize their toon's contribution to a raid, but there's nothing short of an epiphany that's going to make an unpleasant person fun to be around.
The DK off-tank I mentioned previously who was vastly overconfident of his Heigan dancing skills was still a lot more fun than the smartass tank we had to pick up the following night when the DK couldn't make it. When I put runs together, I don't go looking for rude players no matter how competent they are. They make my job harder by being a constant irritant to either myself or other people, and they'll cost me more time having to deal with complaints than I would spend picking up a more inexperienced player who's willing to put the time in to learn a fight.
Peoples' memories for the names of the jackasses among them are also astonishingly long. You may not remember the people you piss off today, but I promise they'll remember you.