This dropped for me (40 holy/21 disc priest) last night after a Oz fight, and it's definitely a raid trink.  Don't bother putting it on anywhere you have less than 3 healers, as an above poster said its purpose is not to make you personally a stronger healer but to make the raid at a whole better at healing.  Unfortunately I didn't get a chance to use it much, as we stopped for the night after the Curator.

The best use as a priest that I've come up with is to activate it and then spam level 1 flash heals on your tank in a boss fight to fully stack the effect.  That would only cost around 600 mana, and a +100 bonus to all healing buff on a raid tank is fantastic.

When you have it time it right you can get about 30 seconds of bonus, and the 2 minute cooldown means you'll be able to use the trinket multiple times on a boss fight.  Seems like it would really shine with several healers all using it in rotation, plausible in 20 to 40 mans.