Also, my fault, I probably should have mentioned at the top this was primarily for PUGs below lvl 60. I ran through Scarlet Monetary-Cathedral 10 times in a row (I needed Library), and the majority of this research came from that, and my times with Black Rock Depths (my most recent encounter with 2 warriors, a druid healer, a lock, and my mage as DPS, had me die over 7 times, included numerous party wipes. The worst was against the Golem Lord, where after getting the go ahead to attack him, he charged straight at me, past the two warriors who were attacking him, and killed me. I also ended up running halfway back before the Druid asked if I wanted a Rez.)

Right now, something that does 15,000 dmg would wipe the whole party, and pretty nicely geared out for my lvl, I’m no where near 7000 HP with my Mage. I think I just clear 3000 with my pvp gear.

Tanks:
Druids…. And they don’t wear plate…
Pallys have to be really good geared to be capable of being healed…

Healers:
“If you’re a priest, get out of shadow form, you’re on healing duty. Are priests the only class that can heal? No, but they are the best at it, and if they are doing DPS your party is in trouble.”
Wow, two wrong senteces…
First: A shadow DPS can deliver quite a powerful amount of single-target dps – so why drop him?
Second: A shadow dps increases all magic damage on his current target by 5%. Oh, and Shadow dmg by another 10%.
Third: A shadow dps grants you mana and health back – to the point of restoring tens of thousands of mp (several times your averaga mana pool!) in long encounters.
Fourth: Whether or not priests are best or not is debated by a lot of people. However, they are talking healing specced priests. Any healing pally, druid, shaman can dunk a shadow priest w/o thought.
Oh, and a healing pally with a shadow priest is one of the most powerful combos for healing and dps you can find for 5 man instances….

“heal [...] the DPS if they aggro”
If dps aggroes – dps dies. Do not encourage horrible playstyles!
When the dps aggroes in later encounters there is nothing left to heal! (Ever eaten a 15000+ hit and healed through that? On a 7k hp mage?)

“In hopefully rare cases you may be required to rez.”
Oh, wait, not all healers can rez. If you’re playing a druid you are essentially out of luck (actually, if your battlerez is free you can rez your 4 friends in just 90 minutes!)

“There are two types of DPS: Melee DPS (the Rogue), and Magic DPS (the Mage).”
And:
Meelee: Off Warriors, Feral Cats, Hunter Pets, some warlock pets (fel hunter, fel guard)
*in between*: Ret Paladins, warlock pet (succubus)
Magic DPS: Warlocks, Shadow Priests, warlock pet (imp), boomkins
Ranged Physical DPS: Huntards

The usual distinction is between meelee vs. ranged.

“While this does mean the Rogue is in front of the healer, it also means its going to get hit”
A good rogue will get pretty much no damage at all.
Sorry.

“I was once in a PUG of Paladin, 2 Priests, 2 Mages”
So, you had what, 1 tank and two healers?
….
Or maybe, just maybe, was one of your priests not quite what you would expect from “the best healer”? So, maybe, just maybe, you needed to take and additional essentially useless person, because you did not have a real healer at all?
Or was it just, that one of your evil priests might have been doing shadow dps after all?

“You guys are Support, which means you’re around to help kill things, but really serve no purpose.”
Wow. I am impressed. I never heard of this role.
*ehm*
Maybe, you just don’t know what to do with those people? Or maybe they just don’t get what to do with their class?

Lets see what you got there:
“The Druid can do anything”
Yes. A druid can do anything – if he specced for it.
“However as the booklet says, [...] they can do anything, but there could always be someone better.”
Sorry man, there is no one better capable of tanking meelee-bosses.
Sorry man, there is no one better capable of smoothing out damage with hots.
Sorry man, owls do more of their share of dps, if you acknowledge their 5% crit aura.

“Shamans also bring a lot to the table. They can melee, cast, and use totems which are very versatile.”
Yeah, so you have got an elemental shaman that does as much dps as a mage and increases the dmg of the mages by roughly 6-10%.
Or you have a meelee-shaman that drops wind fury, increasing meelee-dps (rogues and warriors anyone?) by 10% and does a good amount of dmg – especially burst – themselves.
What the heck makes them “support”?
In may view, you got powerful dps roles?!
Oh, and of course a healing shaman is arguably the most powerful class for healing 5 man instances…

“make sure they know what they are doing”
The one point I totally agree with you.
Not the class makes a good dps-player, but the guy behind it.
I know a ret paladin who does over 1000 dps in T4 – but most other ret paladins have problems keeping up with the tanks…