Josh at E4aE earlier linked to my post about raid buffs and debuffs, and added some concise commentary of his own from the POV of a raiding Paladin. It's well worth reading for every class spec which was previously DPS/Utility rather than straight-up DPS.
I'd sum up the changes by saying "DPS Stacks, Utility Doesn't". There's now no excuse, from a PvE standpoint at least, for different DPS specs to have unequal levels of designed-in DPS for any given raid instance. A shortfall in melee DPS for example makes it very hard for a Ret Paladin to justify his position over an Assassintion Rogue, and so these two classes need to be balanced with comparable DPS over a given raid encounter.
And with that in mind I'll link to Dwarf Priest's Superb Buff/debuff chart. This quick reference guide is great for showing the specs which can bring the utility you desire, just in case you want to stack your raid. Be warned though, it compares the absolute magnitude of the buff (e.g. 2% vs 3%) rather than how easy it is to apply that buff (e.g. BoSanc being better than Grace, or different Aura radii) or spec for it (Heart if the Crusader vs Master Poisoner), so you'll still need to do some research! My only criticism is that utility in one talent tree is labelled as providable only by a class specced totally in that tree, whereas utility in Tier 1-3 can be obtained by pretty much any class spec. For example, Heart of the Crusader is obtainable by Holy Paladins by speccing only 8 pts into Ret (same goes for Imp. BoM). But to effectively label that may overly complicate the chart, so it's swings and roundabouts.
With very few exceptions, come 3.0 any combination of class specs are entirely interchangeable with another combination of class specs with respect to buffing and debuffing. The effect is subtly different depending on the nature of your Raid:
10-Man Raids: For progression in 10-man raids class composition remains important in terms of Healer/Tank/DPS balance, but becomes more open to imgintion. Tuning for all raid buffs becomes impossible, so each buff you do choose to take can make a reasonable difference to your chances of success (though player skill and gear levels remain paramount). 25-man Raids: Stacking raids for Utility takes up around half the possible raid members, with utility from Healers likely being the first accounted for. This means that the other 10+ spots are taken up by classes chosen for DPS and 'Value Added'.
Value Added means the sorts of features which, whilst not necessarily being unique to the spec, gives one class or spec a leg-up over another in any raid setting. These can be obvious, such as additional Rogues for Kicking to interrupt casters or Paladins for Cleanse, or more subtle such as choosing ranged DPS over melee DPS to reduce the strain on Healers or having DPS immune to Mana Burn/Silence effects. Previously other forms of Utility were of primary concern as they tended to add more to the raid as a whole, but with the latest round of changes the value accorded to 'Value Added' rockets.
Those specs which previously had Buff utility but missed out on some of this Value Added, as well as those which now share a Buff/debuff class with Healers, are the inevitable losers in this change. This is IMO especially the case for Melee DPS, where the old 'hybrids' of Enh Shaman and Ret Paladins were deprived tools taken for granted by the 'pure' classes because of their raid utility. The question 'Why Take Ret Paladin' is certain not settled, though some will argue that it never should be settled.
It will be interesting to see how things shake out in Wrath of the Lich King. As always, the individual mechanics of the encounters is key.