I've written here before about how much I enjoy pugging and how 5-mans are still my favorite part of the game, but that was always written from the perspective of a Druid who usually tanked. Even if you're not sitting on great gear, a competent tank can still compensate for a player's having blundered into a patrol, or a pet on aggressive, or someone else's inexperience with the dungeon; they simply adjust and pull with these potential issues in mind. My Shaman, by contrast, can do very little about these problems except attempt to outheal whatever damage results -- and I've learned that I can't always do this. Healers are at the mercy of everyone else's gear, experience, and latency, and it makes a sad kind of sense that so many of them are adamant about vetting potential groups before getting themselves involved.
Maybe my Shaman's luck with pugs will change at 80 with more experience and better gear, but something tells me that if my shammy and not my Druid had been my main, I would have had a very different, and not entirely welcome, experience with LFG.
*Players kept getting one-shot by Ingvar's Smash and the axe AoE. "Why didn't they move out of it?" you (reasonably) ask. I still do not know.