uhm... the big green ones charge the farthest person from them that is still on their aggro list. The lasso spiders do the same. You can limit these abilities with LoS; they'll target the farthest person for a half second, do nothing, then turn back to their tank.
The skitterers, we do that a bit different. We get a tank to put whatever thorn-like trinkets he has on (and druid thorns), get him to pull un-PW:shielded (to get rage). Have every single healer use small heals on him so that no one healer has high aggro, then after enough time for about 8 to 10 demo shouts, put out some light AE from the mages/hunters/locks. In about 15 seconds they'll all be dead with noone taking any damage but the warrior.
We had a string one night where the small patrolling spiders would be split up when we pulled them. Needless to say, they are chained, and the rest of their friends waiting across the room brought more friends and well... you get the idea.
Every time we do double gargoyle packs it makes me extremely nervous and I hate them for it. This might also have to do with the fact that on what was going to be our first Noth kill the patrolling gargoyle respawned, flew through the slime wall and proceeded to AE us all down. There were so many spits on that gargoyle when we cleared back.
LOS pull / pet pull the spider packs. Usually we kill the Venom Stalkers first (nasty green big ones with the 2500/tick poison charge DOT), then followed by the healing curse ones. We usually leave the Scorpion-esque ones until last, since all they do is move people around. Slightly disorientating, but not deadly.
Naxx trash so far is okay. I think good trash mob ideas are ones that can wipe your raid when you learn it, but once you have it down you can clear it quickly and semi-reliably. Mobs like the gargoyles are a good example. First time to get to Noth was long and hard, but now it's cake to get there.
I'm glad to not have found any Anubisath Defenders, but I don't think we're out of the woods yet on those kinds of mob.
The trash after Faerlina is a bit monotonous, if not long or difficult. I'm kind of dissapointed they wasted all that instance room to have what looked like mismatched mobs there.
If I could design trash I would design fights that were quick and painful rather than long and boring.