I don't like divinity much. I should though. 5% more healing should be a good talent, but it isn't.
The problem is with how healing works, or more accurately, how it fails. Rarely do I see a tank die because there was not enough healing output. Instead I see them die because of healing timing. A small heal now which keeps the tank above zero is infinitely better than a big heal a tenth of a second later. Divinity doesn't help with timing.
It will, however, make that small heal bigger. Will that help? I doubt it. Instead it's likely that that timed heal will be followed by several more spam heals which get the tank to full, and a little bit more. In this situation the 5% contributed to nothing but overhealing.
However I must admit that this is based on the assumption that a tank dies in 2-3 hits in Ulduar. Maybe I'm wrong. If damage comes in smaller amounts, heals can as well and rather than 5% being ovehealing, it can be a cancel on 1 in 5 heals.
It all comes back around to my hatred of effective health as a critical matter for tanks.
But what about imp devo aura?
However I shouldn't pick and choose when to use this reasoning. After all, if 5% is useless, is not imp devo useless as well? 6% isn't all that much better than 5%. As I considered this self-critique I decided to recheck imp devo. My first incorrect bit was that it was 3% (I don't know how I managed to forget). The second was that it also has additional armor on it. It's an effective health increase, not just a healing increase.
Furthermore, the healing bonus covers many people. This becomes useful since AoE healing, in my experience, is sometime about output in addition to timing. That 6% can start to have an effect and with JoL it provides a significant increase to raid healing.
Where else would I spend the points?
PoJ for sure. It's stronger than run speed enchants which means slightly better ability to get into position for avoiding fires, getting into range, or moving mobs. Furthermore, this means I can get a different boot enchant, one with more stamina.
Other popular points seem to be conviction and crusade for aggro.
This was only for prot. I have it as ret, I think it's useful. For soloing it means 10% stronger self-healing (5% out and 5% in). In groups it means increased healing from JoL, helping to compensate for SoB. I suppose it's also a boost to DS healing as well.
It's also good for holy, I think. I don't know much about holy.