I just finished leveling my priest from 61 to 80 in the last month. I did a LOT of instances during those levels with a friend who was leveling a mage with me.
For the most part, I really had VERY few problems doing PUG's. Occasionally I goit asshat tanks... occasionally asshat DPS - but largely, my experience was pretty pleasant.
In the last week and a half, I have been grinding out heroics on my priest (usually healing). Again, my PUG experience has largely been decent. There have been a few stinker groups... and I was even called the "worst healer ever" in one particularly crappy crop... but water off a ducks back I suppose.
I actually had a lot of fun leveling my priest from 61 to 80. He had been sitting dormant since the beginning of BC. lol I never thought he'd see play time again considering I didn't like my priest much at 60.