I mostly just read EJ, and i thank you all for your hard work as it has helped me improve alot as both a priest and a mage. But i've decided to post seeing as this guide (and forum) is lacking on actual stratagies on disc priests, and I hope I can help.
Disclaimer: I'm not a pro by anymeans, just trying to start a discussion and try to fill in this guide. If my methods are just wack, don't rail on me >.< I also want to appologize for the horribly named tips, and cheezy descriptions.
Discipline is all about shields. Throwing shields (PW:S), Procing Shields, (Aegis), Making the tank's 'shields' better (Inspiration), even getting mana back from shields! (Rapture). Use them often and wisely.
3.1 Note: This stands even more true due to Soul Warding. No CD and 30% reduced mana.
2) Everything runs on Borrowed Time:
Borrowed Time really is the best thing about being a discipline priest. Penance may get all the glory, but BT does the grunt work. It allows you to drop the 5 points in Divine Fury for Imp Renew and Healing Focus. Tank low? Through a shield and get a quick GH out. Party low? Pop a shield on a tank and grab a PoH*. 25% haste is a boat load. With a 4 sec cd, BT should be how you are getting your GHs out, not Divine Fury.
*I added this as this will be Disc's CoH come 3.1 With PoH being able to heal another group (finally!). BT + PoH will be the bread and butter raid healing for disc priests.
3) It's time to Flash your Buddies and get some (mana) beads.
Flash Flash Flash. A faster cast time with Flash means more chances to procs Aegis, which means more healing and mana for you.
3.1 Note: Imp Flash Heal! Woo. 15% mana redux, 10% increased crit on <50% health targets. More shields and mana for everyone!
4) C-C-Combo Breaker.
Shield, GH, Penance is your bread&butter move for tank healing. Toss a PoM and Renew after it, and leave him alone to focus on other things. You may also throw in a PS between Shield and Gh if the tank is super low.
This brings me to my final point. Disc is a very different type of healing than Holy. Holy is very preemptive. Disc however, is reactive. While you never want to be sitting still, throwing shields on a tank at full health wastes the weakened soul debuff and borrowed time IMO. Let the Pallies pre-heal. Disc priests are the only classes that can essentially stop incoming damage. Use this to your advantage! Toss a FH or Renew on a damaged DPSer, Just be careful not to get caught in a GCD, or even worse, a shield CD!
Thats what I got for now. Even if this is all trash, at least it will start some more discussion.
[A note about the last section. After re-reading that i also realized this is also an issue of the diffucluty of raids. If tanks can die in 2-3 seconds like some pre-wrath bosses, reactive healing just isn't safe. We will see how this works out in Ulduar]