It looks like Blizzard is on a stealth-nerfing spree the week after Cataclysm's release. It started with guild experience gains being nerfed, and now today Nethaera posted to confirm nerfs to Holy Paladins.
"Mana is supposed to matter for healers, and in the case of Holy paladins, that just wasn’t happening. We were seeing raid groups attempting to learn new bosses where the other healers were out of mana while the paladins were still at 90% of mana," she said.
It looks like the major focus of the nerfs are to Light of Dawn -- reducing its level 85 healing amount from 2600 to 1700 per Holy Power -- as well as a change to Tower of Radiance. Holy Light can no longer generate Holy Power when cast on the player under the effects of Beacon of Light, meaning you'll need to rely on the more inefficient Flash of Light or Divine Light spells to continue to fuel Light of Dawn usage through this method.
"The main culprit for the increased paladin efficiency this was Holy Power from Tower of Radiance. We were seeing a strategy develop where paladins would cast Holy Light on a Beaconed tank, and then cast Light of Dawn on the raid (and use very few other spells)," she contiues "This strategy was remarkably successful considering how simple it is. The Holy Power-based heals are supposed to be an important component of the paladin kit, but because Holy Light is designed to be super efficient, the overall strategy was too efficient."
Another reason Light of Dawn was nerfed is due to it eclipsing Word of Glory -- making the latter very unattractive to use.