First off, Disc priests are not necessarily tank healers.
In fact, we are quite possibly the best raid healers out there for current content. We have our limitations and problems but generally we're amazing. I will just assume they'll put you on bubble duty eventually because that's what all Disc priests do nowadays, at least from what I have experienced.
That being said, from your armory I can see a few things you should change.
I'll assume you aren't going to fight the Lich King all too soon, so I'll tell you what I'd change gemming and enchanting wise at your current point of progression. You don't want any spirit gems. You obviously need one blue gem to activate your meta, use an
SP/MP5 gem wherever it gives you the greatest socket bonus (and ignore socket bonuses that aren't spellpower). For red sockets, keep gemming SP, for yellow switch to
SP/Int gems gradually as you see fit (if you find yourself running out of mana, get more intellect). Seeing as you are a tailor, get a
tailoring cloak enchant and the
cheap leg enchant. Seriously, I wouldn't even have let you into a raiding guild without everything enchanted properly.
Now then, as you progress through ICC you will find that later boss mechanics enable you to
exploit Rapture to a point where you don't need any throughput anymore and where 75% or more of your healing will come from Power Word: Shield.
This means that you only need haste till your GCD reaches 1s (which is at 5% with raid buffs, so ridiculously low), crit becomes almost completely worthless because your most important spell cannot crit, and mana regeneration becomes a complete non-issue. Which means you want to gem for spellpower and spellpower only down to the
meta and also get a new
cloak enchant. This will probably get relevant at Sindragosa at the earliest, mostly it's just a better option for the harder hardmodes.
Your talent spec is also definitely not the cookie cutter for raiding.
This is what it should look like by the book, there really isn't much choice. You do
not want Divine Fury as Disc as GHeal is really pretty much worthless unless you take all the GHeal talents (thinking Serendipity here), and Penance, ProM and PW:S are still much much better in every way.
Now you can vary stuff a little bit. You can move the talent point from Desperate Prayer into Absolution. You can move the same point as well as the Healing Focus ones into Spell Warding if you want to be a bit more defensive. You don't really want to change anything else.
Spell priority is as follows: Power Word: Shield is your most important spell by far. Use Prayer of Mending as much as possible, too. Really
do use it every time the cooldown's up on fights with heavy and constant raid damage like Festergut. Penance is good when you see your tanks drop too low, I find myself using it as often as the cooldown allows on a few fights. It's also awesome for Valithria.
Feel free to use Flash Heal whenever you have breathing room or someone really needs some healing urgently and has Weakened Soul.
If you have breathing room, you can also Renew the tanks.
Don't forget about Divine Hymn! It's awesome for BQL heroic, for example. You should also keep an eye on your other healy/mitigating cooldowns. And Power Infuse the Holy paladins (they are our friends), they love it! Or DPS casters, when there isn't any need for more healing.
Now, that is how I do it and there are some variations since we don't have a set rotation for most fights, but in any case I generally suggest looking at what better Disc priests than you are doing and looking at their logs over on World of Logs. And that tells me that I'm doing something very similar to the Disc priests in the really high end raiding guilds, so I don't think I'm completely wrong here.
Edit: Forgot a couple of things (you're probably thinking of gagging me by now, but it needs to be said).
1. Look at your own logs, and learn from them. Are you using every GCD? Do you find yourself not using Prayer of Mending as much as you thought?
2. IMPORTANT! Welcome to Disc, enjoy the ride.
Edited, Jun 30th 2010 4:39pm by Kalivha