Short version: In Cataclysm 10-mans, a raid can only use one CR per encounter, and in 25-mans, the raid can use three.
That means that leaders will have to manage the CR’s better, and the raid will have to be much-much more careful. Interesting change if you ask me, but I do not get what is this good for. Also I am sure that this will cause enormous QQ on the forums (as nearly every change does though).
Some response from a creative druid on the forums:
I think this is silly. I was totally planning on doing a 10man all druid raid so we could all get hot plate drops.
Long version after link.
The design for combat resurrection effects has changed a good deal for Cataclysm, and we want to make sure players are clear on how spells like Rebirth and Create Soulstone now function. Rebirth has a 10-minute cooldown and Create Soulstone has a 15-minute cooldown. On raid boss encounters, you can only use one of these combat resurrection spells (so one Rebirth or one Soulstone) per attempt for 10-player raids. For 25-player raids you can use three forms of combat resurrection per raid boss attempt (so three of any combination of Rebirth and Soulstone). The count is incremented as soon as a player accepts a resurrection, so one can always choose not to accept if he or she wants someone else to get the resurrection instead. There is no equivalent of the Sated debuff (which tracks Bloodlust/Heroism usage), but you will get an error message if you try to resurrect too many players, and we might add tracking to our raid interface if there is demand for it. Outside of raid content, you can use as many battle resurrections as you have available.