Blizzard stated before, that they aim to make spirit a better stat for Disc priests, that we know. They also wanted to make it "more attractive" for mages, and they did.
If I where a mage, I would be very happy with a SCALING spirit ability. But they went all out on QQ, and gues what? The spirit scaling was not only buffed in a major way, but they got a free 3% crit as bonus!
Now I don't want to come off as a mage hater, I love mage water :P This is just an example.
Now to the point:
1. Holy: this spec scales well with spirit. The 25% spirit = spell power is nice.
2. Disc: does nothing with spirit. Zero. They nerfed the crit based mana regen, nerfed the spirit mana regen... So we have to stack lots of spirit for little regen and get... you know...
3. Shadow: has lots of spirit on set gear, it's the same thing as with mages. We get 10% spirit to spell power... this is not enough. 500 raid buffed spirit is 50 spell power, come on... We can glyph for more scaling (like mages with armor glyph), to get a random proc to get another 10% scaling. I see two things wrong with this: the random aspect, this is not a constant buff and goes away when we stop dps for a few seconds, then we have to wait for it to proc again. It's fun. It's a nice gimick. But it should be a bonus thing, not a "must have to get scaling glyph". The other problem is that when we get a better glyph (and we will not in 3.1), the scaling will be no more... Not to mention that we only have 2 dps glyphs ATM.
I was REALY hoping that Disc priests would get the change mages got. Spirit scaling with crit would be very nice for disc priests and would fit well with their mechanics. I don't have to tell you how vexed I was when I saw mages get that change. Also spirit scaling with HASTE would be nice, maybe a good idea for flash heal spamers that we are
As for Shadow I think that spell power is perfect. But I would like to see more base (talent) scaling with spirit. If indead PTR shadow priest DPS is to low (and it is reported to be 1-2k below others), then adding more scaling from spirit would be perfect. Maybe it would make Imp Spirit Tap a little more then a mana regen tool. (No it would not actualy, but still it would be a nice combo). I would be sad to see blizz try to scale priests in some other strange ways.
Do you think Blizz will change something with this? Or have they forgoten that priests DON'T LIKE spirit too? I have seen posts made by mages saying "leave spirit to priests, thats their thing!". Why the hell is it our thing? The Shadow spirit scaling is crap, our best in slot items don't have spirit. Well no, we like spirit to be honest, it's just not good for us, and we would like it more if it would like us back