I used to PuG a lot. Like, all the time. This was at a time when ICC had just come out, ToC was already old news and my guild at the time was still struggling with Ulduar.
Even after joining ICC-level guilds, I used to run a lot of 25man PuGs since the raid lockouts were separate. They usually didn't get past the first 5 bosses in ICC, but that was fine with me, you still got your frost badges, a couple pieces of gear and maybe even a shoulder tier token. Things were good.
Then they merged the 10/25 man raid lockouts and effectively killed pug raids, in my opinion. I've done a single pug since then, and was later given a huge guilt trip for pugging one boss in Firelands. Sigh.
Now I hear that Raid Finder, similar to the Dungeon Finder, will be available soon. All I can say to the people who will subject themselves to that level of torture...good luck with that.
If the random dungeon finder was any indication, random raid finder will be 100x worse in terms of bad behavior and general fail. Currently you see people ninjaing and then raging over ilvl 333 gear. How do you think the said ninja and rager will react over ilvl 359 gear? It will be a disaster!
I think they should only let you pug the previous tier's content, but that's almost a moot point. I don't think a completely random pug has any chance to down relevant patch content. I'd actually be shocked if a randomly chosen pug made up of the average player you see in a random dungeon could even down a significant portion of Firelands trash.
Basically I imagine this kind of scenario:
Raid leader: Ok guys, everyone knows this fight right?
Healer: Wait let me drink, I'm oom.
DPS: Cmon guys I'm in a hurry gogogo
Tank: Ok pulling
Healer: Wait! I'm getting mana!
DPS: Too late I MD'ed tank
DPS: Oh crap I pulled the trash! *FD's next to healer*
Healer: I'm dead!
DPS: Brez him!
Raid leader: Brez!
Everyone: Brez brez brez!
Healer: DK why didn't you brez him?
DK: What's brez? I don't have that spell.
DPS: Ooh that trash dropped a BoE tank sword
Hunter rolls need, wins sword, drops group
*everyone rages, calls names, then leaves*
That is actually a combination of several things I've witnessed in a random dungeon.
I might join a couple PuGs on my alts, just to lol at the fail...