i've had 2 unhappy instances using the dungeon finder.

1) a ret pally needed with me and won the spell dmg necklace from H FoS
2) in H Occulus, ppl were doing god awful dps and were making a whole bunch of mistakes like misspulls which i had to pick up (was tanking) and then the warlock had the nerve to say "God lets go already". I left immediately when he said that.