Yes, you heard right. MP5 is being removed. It will be gone. Fist pumps and high fives all around!
In any case, when the next expansion comes around, everyone will need to relearn the entire mana regeneration mechanic. Thankfully, it should be much easier this time around. Spirit is the main stat which will contribute to mana regeneration since intellect provides spell \power. It is too early to provide any advice or guides since we can't actually see the changes in action just yet, but the basic idea is that healers will be stacking a combination of intellect and spirit to increase healing throughput as well as mana regeneration.
Lastly, for the druids and shamans:
I wonder if this means Prayer of Spirit will be removed. All in all, I'm very excited about the regeneration changes. It'll make things much easier for players to understand (like me)!
Anyway, the line of thinking here regarding the removal of raid spirit buffs is this: Since spirit will be providing elemental shamans and Balance druids with hit due to a talent conversion, any raid buffs which boost spirit will presumable bump their hit and put them over the hit cap which isn't a good thing since any surplus points will be considered wasted.
World of Warcraft: Cataclysm will destroy Azeroth as we know it. Nothing will be the same. In WoW.com's Guide to Cataclysm you can find out everything you need to know about WoW's third expansion. From Goblins and Worgens to Mastery and Guild changes, it's all there for your cataclysmic enjoyment.