This last month I've been doing more shrouds than I normally do. I went down to 1-2 a week and concentrated more on epic quests/raids, because my stockpiles of larges were considerable (30 large scales). The ones I was running were often closed groups from specific invites. However, I've been doing them a bit more lately. I don't lead these raids myself anymore on normal difficulty, as they are quite easy, so I've been joining PUGs.
Anyways, I've found that this is a pretty good way of identifying bad/obnoxious players to keep them out of the more challenging raids. This is in conjunction with identifying the good ones as well. I have also noticed you get players that will drop group with little provocation, or just drop after part 4 when they know its a completion run. I've added more toons and guilds to my "friends" list this last month than I have in the previous 3 months. I had a particularly bad sorc last night, that prompted this observation.
Thought I would share this. Seemed a partcularly useful strategy considering you run the shroud anyways. It still is a balancing act between extra time in a PUG shroud vs. meeting new players, but I like meeting new players and it seems you get a different breed in the shroud (maybe its just because I don't put those together myself anymore). I tend to run the PUG shrouds on my healers, as A) I can ensure completion even in bad groups almost all of the time, whereas you can't on DPS, caster, or bard spots and B) you can wait to the end to join and not have to wait at all to get started.
I hope this doesn't sound too elitist, but I've found my enjoyment of the game is enhanced by an up-to-date "friends" list.