I have a low opinion of Heroic PuGs in general. I never PuG a tank or healer, but I'll sometimes recruit DPS in the knowledge that there's only so much they can do to screw up a run. Friends are an entirely different matter. I'm more than willing to accept players that my party members may know already and have experience with. But taking a PuG tank or healer is simply asking for hours of time spent with nothing to show for it but a repair bill (or ninjaed shards, in the case Heart mentioned).
If it's a normal run, I can tank 90% of the mobs on Lealla if I have to, so I don't worry about it too much. Then again, I have nothing to gain from normals, so I'd only ever do one to help someone out.
I remember several months ago, when I got asked to go to a Heroic Hellfire Ramparts with someone who wanted to finish an in-progress run. It turns out that the Druid who was doing the inviting had been kicked out of a run prior to Nazan, and his "buddies" finished it without him. When we zoned in, we all got saved to a completed instance, which we didn't realize until we went to Nazan and found him not there. Needless to say, that Druid went on my ignore list after I had a few choice words with him.