In the hope that I'm not stepping anyone's toes in posting this, I thought I'd go ahead and cross-post an FAQ that I did in preparing for the patch today. I did't see anything up with regards to 5.0.4 yet, and with the patch day at our doorstep I thought it might be useful for people looking for information. If I've made any errors (possible!), kindly point them out to me and I will be happy to correct them. Additionally, if you think anything needs to be added, also point it out to me and I will be happy to make the addition.
How Should I Spec?
I think the first question that is on the forefront of everyone's mind is "what do I do with these new talents". The new talents are such that the intention is for one not to be exceedingly better than the other, which leaves you many options. You should explore the talents, and find ones that suit both your play style and the dynamics of each encounter. With the ease of respeccing, you may find that certain talents are more advantageous for different encounters. As such you may want to consider using the new flexibility to respec based on the demands of each encounter.
Here is a basic "generic" spec that will get you started in the right direction.
What haste breakpoint do I need?
Since we are still at level 85, and most of our pertinent abilities have remained largely unchanged, our haste breakpoints will remain the same at this time. You will still want to have 2005 haste. Keep in mind, however, that you will be losing your idol. So if you had any haste on your idol, you will want to be sure to find somewhere to reforge or regem so that you are at 2005 again.
Do I really only have 100k mana?
You do! You will also be losing revitalize as a source of regen, replenishment has been removed and intellect no longer has an effect on your mana pool or regen. From my play on the beta, I think that you will probably feel the pinch a little, but not an extraordinary amount at level 85. If you find that you are running out of mana too quickly during encounters try backing off of your rejuv use some. If that still isn't sufficient, reforge some spirit back onto your gear. I ran at about 2600 spirit at level 85 on the beta and utilized a heart of the unliving, so if you are one of the players who dropped down below 2000 you will likely want to reforge some of that spirit back before stepping into your first post-5.0 raid.
So what, exactly, does Intellect do now?
Intellect will continue to give you additional spell power, as well as increase your critical strike.
What do I use for regen?
Spirit will be your new regen stat. As you move into MoP you will need to find a balance between spirit and intellect that feels good to you, and will be subjective to each player. I don't think you will need to make drastic changes at 85, but if you are running with an exceptionally low amount of spirit, you may find that your mana cannot keep up with the way that you are used to healing.
Will my Stat Weightings Change?
Outside of perhaps wanting to add more spirit if you are low in that area, your stat priorities will remain largely the same at this time.
What Glyphs Should I Use?
For major glyphs, I have been favoring: Regrowth, Wild Growth and Lifebloom. If you are uncomfortable with the change that the Regrowth glyph brings to Regrowth, I'd recommend using the Rejuv Glyph. With Rebirth at a baseline 60% now, you no longer need the rebirth glyph as a "must have".
For minor glyphs, the world is your oyster...or something like that. Pick whatever you want! I like the orca and stag glyphs quite a bit!
What about this new Iron Bark thing?
Use it, love it, keybind it! It's on a relatively short cooldown and off the global cooldown, so I would recommend using it often and not waiting for the "perfect" time. I would recommend making a power aura to remind you when it's available. Additionally, don't forget that you retain barkskin and they do not share a cooldown.
What about these new Mushrooms?
Mushrooms are here to stay. My recommendation is to get used to using them by finding ideal time in your raids to both plant them and explode them. Explore them and make a decision on how you feel they work for you. Make sure to set comfortable keybinds for both placing and detonating your mushrooms. I personally have my drop mushrooms keybound to "shift-r" and my detonate to "shift-t". I'm not saying you should use those exact keybinds, but with the way you must target placement of mushrooms, I do strongly encourage you to have it keybound. Note: detonate is now on a ten second cooldown (up from the six it was in earlier beta builds).
What about Lifebloom and Harmony?
Both of these abilities have had their duration increased. Lifebloom is at 15 seconds and you only need to activate harmony once every 20 seconds. You may find yourself refreshing the abilities long before it is needed, out of habit, but with proper tracking of them I imagine new habits will be formed.
Can I still dispel?
Yes! However your dispel is now on an 8 second cooldown. You may want to consider making an aura for it.
But how will we be able to kill Spine or Sinestra?!
Don't worry! Blizzard has already thought of that. The debuffs on Heroic Spine will turn into the "friendly" debuff after only one cleanse (which will make it more challenging to get onto your tanks - so you may want to anticipate them taking more damage). For Sinestra, each time you cleanse wrack your timer on cleanse will be reset, so nothing will change about the cleansing aspect of this encounter.
Will the way I heal change?
Largely you will heal the same way. Our core toolkit has not changed much at all, and so the way that we heal remains very similar to how it is currently. You will want to try to work in mushrooms and if you find that you are struggling with your mana, you may want to use rejuv a little less. But largely I think you will feel fairly comfortable with your toolkit post 5.0.4.