My level 49 Emp/Rad Defender gets LOTS of invites, many of them blind. I accept most when otherwise unoccupied, and am pleasantly surprised on a regular basis by the quality of many of the groups I join. The ones that are PUGly get dropped by me very quickly.
I know I'm on a good PUG when I get complimented on the quality and timing of my buffs/debuffs rather than constant yells of "HEAL!"
I know I'm on a good PUG when people recognize that I know how to do my job, and allow me to apply Fort and AB to the key members that need it most.
I know I'm on a good PUG when the leader takes control, the team does their jobs, and I can spend almost as much time using my offensive attacks/debuffs as I do my heals.
I know I'm on a good PUG when the hours roll by, the AV's go down hard and fast, and I can count the number of team deaths on one hand.
Many of these players end up on my "friend" list quickly, and I know I end up on alot of theirs...