We don't know. We know that some stats, such as defense, are going away. What will happen to the other stats as a result of that is unknown. Blizzard has said some stuff about Cataclysm itemization, but we don't know nearly enough to begin talking about it with any real knowledge, and we certainly don't have enough to begin critiquing it.
We do have an extra tier of gear now, more or less, because of stat inflation -- particularly when it comes to tanks. Tanks reached the "I'm invincible" level way too early in Wrath. In BC, it took a tank fully geared through Illidan to feel like there were times he was invincible, and then he really only felt like it when he cleared Sunwell (and very few tanks go to that point, especially with regards to not needing any gear from SWP). Nowadays, you can get a tank geared up and roll through nearly all content just through the five-mans and iLevel 232 gear. The 251/264/277 gear from Icecrown Citadel really is overpowered in terms of tanking stats, which is why Icecrown Radiance exists. And of course, as the tank's gear increases, so must the other player's gear. It's a vicious cycle, one that Blizzard has, in my opinion (and in some of Ghostcrawler's comments), failed at in Wrath.
But will they fail at it in Cataclysm? My money is solidly on no, they won't. They are very smart people and know their own mistakes better than we do. I'm sure they're very well aware of gear inflation and itemization concerns, and won't let the stats run wildly out of control as we're seeing now.
The other thing to remember is that "epic proportions" is a very psychological term, if you will. Wrath gear feels epicly disproportionate compared to Vanilla WoW gear, but that's because we're so far ahead in terms of content and item level. But if you compare Wrath gear to gear that you'd get out of Sunwell, it's not that far off. No where near as big of a difference as Kara gear was compared to Old Naxx 40 gear.
Blizzard folks did say at BlizzCon (I think it was Ghostcrawler or one of his team) that ICC gear will be good enough for the introductory raids in Cataclysm, which is how things worked in the BC to Wrath transition as well. Sunwell gear was good enough for Naxx 25; the only piece of SWP gear I replaced from heroics was a stamina trinket. To me, you can infer that the 40%+ crit you get from gear now will drop down to 25% or so at 85, which is a nice number for introductory raids. Also remember that Blizzard can (and has) change the formulas for rating->result, so where you might expect it to take 100 crit rating to get 1% crit at 85 in today's formulas, Blizzard could easily modify it and add more to the piecewise function and make it so you need 150 crit rating to get 1% at 85.
Finally, I need to stress again, that even though we can analyze to death what has happened in previous expansions, we can't really be critical of Blizzard or even talk more than speculatively about Cataclysm yet. Until we start seeing gear from the beta, we just don't know.
"What do you think the chances are of getting someone from your own guild through the LFG tool? The other night two of my guildmates and I were grouped for some randoms, queued as party, and the healer we picked up... was our guild's main resto druid."
It's a pretty low chance. I average five to seven random heroics a day, and I've only gotten someone I know in them once. I think it really depends on how active your battlegroup is with the random dungeon finder, and then how big of a tank or healer shortage you have. You are, I'd say, more likely to have a tank or healer you know (or from your guild) based on their relative scarcity.
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