As this post is likely to be deliberately misinterpreted by a certain brand of troll, let me start with this statement: I am very much in favor of Cataclysm making World of Warcraft harder. I specifically like the changes that make healing more tactical, where the healer has to make intelligent choices not only who to heal, but also which spell to heal with. But I also welcome the return of crowd control, and the necessity of careful selection of your target, instead of mindless AoE damage.
Having said that, in spite of preferring situation B to situation A, I'm a bit worried about how we will get from A to B. While I don't like blanket statements like "WoW is too easy", it is certainly true that the excessive rewards for heroics in Wrath of the Lich King did lead to groups being generally overgeared for the heroics they were running, which in turn led to extremely careless gameplay habits. Not so much for the tanks and healers, but very much so for the damage dealers. Not only have they forgotten all they ever knew about crowd control, but in many cases they barely know about how to intelligently select which target to attack any more. If you can kill everything with AoE spells, that is what you will do. Furthermore the excessive use of addons like Gearscore and damage meters has led players to believe that the best damage dealer is the one on top of the damage meter. That is likely to cause problems in Cataclysm.
In the overgeared situation of WotLK heroics, the normal situation before patch 4.0.1 was that the tank could hold all aggro, whatever the damage dealers did, and the healer could keep everybody topped up to maximum health whatever happened. That situation where failure wasn't an option is about to change. Patch 4.0.1 already made the aggro holding part much harder, and healing will become harder once people level up and stop being insanely overgeared for the content they are running. What is the typical damage dealer going to think when his group just wiped? Will he think "Oh, I shouldn't have used that AoE spell while the tank was still charging!"? Or will he think "Stupid fail tank didn't hold aggro, stupid fail healer didn't keep me alive!"? My guess is the latter.
Damage dealers need to learn that failure not only is always an option in Cataclysm, but also that they now carry a big part of the responsibility for that failure. Be that from crowd control or from targeting, a good dps is not just the highest number on the damage meter any more. Too bad I doubt that anyone will ever program a good performance meter addon which gives out bonus points for crowd control and big penalties whenever a damage dealer pulls aggro.
Unfortunately the most likely outcome for some time is an endless wailing of dps players about how bad the healers and tanks are. And that leads me to fear another problem: An increased tank shortage. Let's not mince words here: Tanks got shafted by patch 4.0.1, and there is nothing to suggest that Cataclysm will improve their situation. My healing priest is dual spec and his damage output as shadow increased from 3.5k dps to 4.5k dps with the patch while wearing his healing gear!!! My protection warrior deals only half that damage in his tanking gear, because replacing defense by dodge didn't change the need for tanks to carry around two sets of gear. And melee damage took a big hit compared to spell damage in general in patch 4.0.1. As a result I would need to gear up my tank twice as long as my healer, and still not get close to the same damage output in my second spec. And as tanking already has become a whole lot more difficult, playing a tank just isn't fun any more: He is worse off now both in group and solo gameplay, and gets insult added to injury. While druids probably will remain popular, due to more races available to them in Cataclysm, and their now much overpowered moonkin damage output, paladins will certainly drop from the top of the popularity table, and warriors risk falling down to the bottom of it, with only Spinks remaining as protection warrior.
I do hope that with time all this will balance out, in part by Blizzard improving the balance between spell damage and melee damage, in part by people getting used to the new realities and learning how to crowd control and watch aggro. But until we get there, I'm afraid we can expect some unfriendly moments in World of Warcraft.