Major Blizzard post on the future of buffs and debuffs. A snippet:
For the most part, what this change means is that many buffs and debuffs which were previously allowed to stack together no longer can, and that many buffs and debuffs which only a single talent specialization could bring can now be brought by multiple different specializations.
Essentially, there are about 30 categories of group buffs and debuffs. The buff/debuff in each category can be provided by different classes, making raid construction much more flexible.
For example, Devotion Aura will now provide the same healing bonus as a Druid's Tree of Life Aura. So if you don't have a Resto druid, you can still get the same effect with a paladin. This change also extends to mana batteries, with Shadow Priests, Retribution Paladins, and Survival Hunters providing a similar mana regen buff to the raid.
I think that, on the whole, this will be a good change for the game. There are some posters at EJ however, who feel that this will lead to a new form of raid stacking. Essentially, you figure out the minimum number of characters to cover all the buffs and debuffs, and then stack the rest of the raid with the flavour-of-the-month DPS class.
This is a possibility. However, in my view, there are essentially two types of raiding guilds: guilds which have access to multiple characters of every class and spec; and guilds which don't. Maybe the first type of guild will stack, but they would have stacked anyways. But this change will make life a lot easier for the second type of guild, allowing much more leeway in recruitment and raid make-up.
There are still some issues to be resolved, including mana regen for Retribution paladins, Blessing of Wisdom, and how Judgements (especially Judgement of Wisdom) will be affected.
Edit: Also, just eyeballing the list, Blizzard might want to consider baselining Blessing of Kings. It looks like the only category with a single buff that is a talent.