I've generally had pretty good luck with PUGs. I'm a patient easy-going person though, and I really don't get that upset if we fail the mission. Oh well, that's life, I'll try it again tomorrow night. Overall though, I've found that about 75% of my PUGs will complete the mission just fine.
I get upset with folks that can't follow simple common sense directions. I understand that you may not have done this mission before and I also understand that you might be a new player who just isn't very skilled yet playing the game. I have patience with these folks. The ones I can't stand are.....
1. Leechers and quitters. As soon as you warp into the mission, they go AFK, or in the case of one ranger on our 3 man UW trapping group, as soon as we warp in he said his Dad told him he has to get off the computer now. Bye. If you don't have time to finish a mission, don't start it.
2. The Level 6 Warrior who doesn't understand why you won't accept him for the Viznuah Square mission. "But, but, but I'm a GOOD player!!!!!!" Sorry, I expect a minimum level for certain missions and if you're not there yet you obviously skipped portions of the game and got a run straight to the mission town.
3. The level 13 ranger that did end up joining that Viznuah Square mission. (It wasn't my decision to reject him or I probably would have). I happened to be playing a ranger as well and as soon as the opening mob of afflicted started attacking this guy took the opportunity to whisper to me..."Cool bow and armor! Can I buy your bow and do you have extra armor I can buy?" I was too busy shooting monsters to answer so he kept it up.
"Answer me, I want to buy your bow"
"Sell me extra armor"
"Answer me"
"Are you there??"
<opens trade window>
<I shut trade window>
"I need armor. Trade me!!!!"
<opens trade window>
<I shut trade window>
"I have money. I'll pay you 5k for your armor!"
<opens trade window>
<I shut trade window>
When the mob finally dies I answer him in open chat not to try to trade in the middle of a fight and oh btw, you
CAN'T TRADE ARMOR!!!!!!!!
4. The Mo/W who joined our "GLF Monk for FOW" group. Monks are in short supply here and we really needed a healer. We asked for his build and he said he was a healer. He didn't ping his skills. Actually this may have even been before the skill pinging was implemented. Once we warped into the fissure I noticed that he was carrying a Fiery Dragon Sword. He also pinged "I'm wielding a Fiery Dragon Sword of Fortitude and a Shadow Shield"

Not a good sign.
We engage the first group and of course the first guy into the fray was our trusty monk and his precious FDS. Turns out he had all warrior skills on his bar + healing breeze. But, because he is a monk with healing breeze he insisted that he was indeed a healer!
I know a lot of you are saying to yourself, these people are exactly why I hate PUGs! You are going to find all types in PUGs. If you're the leader you can weed out the bad ones just by asking a few questions before you start. If you're not the leader then get to know the leader before starting. Find out what he expects from the team. If you are the type who needs to finish the mission + bonus/masters and will get mad if you don't then I recommend that you should be the leader and make sure your teammates have the same lofty goals.
The trick to finding a good PUG is finding people with the same mindset as you. If you want masters, advertise for folks who also need masters. If you just want to explore the area and have fun then advertise for a "fun laidback group". I did that in Urgoz last weekend and had a very good time.