I am a healer with relatively fast queues and i find maybe 1 out of every 3-6 groups when i random queue is actually capable of completing most encounters in heroics. I dont know how you guys do it with queues as long as they are for DPS. I would shoot myself if i had to wait that long only to join a random and most likely have it fall apart.
I have been healing and playing this game since the open beta before vanilla wow all on the same toon. Guild groups go just fine, even trade chat groups go without a hitch. it just seems every time i join a random heroic it is god awful, and people afk, pull agro, tank doesnt know the fight, people split dps, DPS fail at DPS, tank doesnt pick up adds on encounters, you name it, in a random dungeon it is a common occurrence