Ghostcrawler did battle with the forumites this weekend, and the topic of discussion was the recent mana changes. Players are saying that the changes (including the BoW and Mana Spring change last week) are basically forcing them to bring more healers along to larger raids, and GC in return expounds on the raid balance that Blizzard is aiming for lately. Interestingly, it's not the 5 healers / 5 tanks / 15 DPS that you might think it would be -- Ghostcrawler says that if they aimed for that makeup, bringing more healers would often make the fights inconsequential.
He goes on to say that the way the fights are designed, you aren't supposed to run out of mana, as long as you're dodging the AoE and are geared up correctly. Making mistakes in gameplay digs into your mana reserves, and so when Blizzard nerfs mana regen, they aren't just trying to make things harder, they're trying to take away that extra breathing room that you get around errors. They don't want healers just healing through damage -- they want people trying to avoid it in the first place.
And, if guildies won't get out of the fire, and your healers keep running out of mana because of it, it's time to weed out the ranks a bit. Finally, GC adds what we've heard before: those looking for a tough battle in Ulduar likely won't find it right away -- the instance is designed to be only a little harder than Naxx. But the hard modes are where the difficulty will really ramp up. If short, says GC, if you don't have enough mana on the easy modes, it's not Blizzard's design: it's the way you and your guildies are geared and playing.