I do not understand this whole Int versus MP5 debate. Let me start off by saying that I've played a paladin since day 1 Burning Crusade. I've raided as a holy paladin through every content since then - all of it pre pre- nerf.
I think most Paladins seriously devalue the benefit of Haste.
Int versus MP5 is not a debate. I don't think there has ever been a doubt regarding which is superior.
-Glyph Of Lay on Hands - gives you back 3900. Does it still work on the PTR where casting it on yourself grants more mana back? I haven't checked.
I'm trying really hard not to be sarcastic here, but seriously ... did you honestly think that these were news to people here? The condescending tone doesn't really help whatever case you're trying to make when it appears that you haven't even made an effort to read through the thread. Believe it or not, we're not blithering idiots who all forgot that mana potions and shamans existed.
I really think most paladins simply aren't utilizing all of the mana return things they have at their disposal. I've raided with other Holy Paladins in WotLK that stack int and I notice that most of the time they don't even bother to Divine Plea - and they don't have to!
Seeing as Blizzard is nerfing my "Portable Shield Wall" Divine Guardian spec, I'm probably going to be speccing back into 51 Holy 20 Ret in patch 3.1. With this build, Holy Light and Holy Shock get +19% crit. With raid buffs, you're easily looking at 45%+ chance to crit with Holy Light and 55%+ chance to crit with Holy Shock - without even gemming for crit!. Oh, and, did you all forget about Sacred Shield giving you +50% crit with Flash of Light? It's practically more common to get a critical heal than a non critical heal.
Again, I think we're all still aware that sacred shield exists. Utilisation of Paladin mana regen mechanics, more often than not, scales very well with Int, which is why it's stacked. Believe it or not you aren't the first person to come here and suddenly 'reveal' that haste is Godly and anyone who stacks Int is an idiot. Read back through the thread and try to find some new arguments; simply stating that haste is great because it's more HPS and "I never go oom!" is not the news flash that you seem to expect it to be.
Getting that crucial heal in .2 seconds earlier could definitely been the difference from a wipe to a kill.
So could a HL hitting for 12k instead of 6k because you don't have to chain DP to maintain your spam. So could the fact that you're melee'ing the boss instead of prepping HLs and cancelcasting on the tank. This is not really a valid argument. I will grant that I think haste is an absolutely fantastic output stat simply for its ability to de-stagger healing, but it's not the 'stack this and tank will never die!' miracle cure that you make it out to be.
The bottom line is that right now, content is ridiculously easy, and anything works. This has been said time and time again but it's ultimately where the differences in opinion stem from. People see that their way works and assume that it's superior. In the current climate, where a 4 minute fight is a marathon, tanks are taking 5-7k hits at the most, and the raid has done encounters so much that they could dodge the fire in their sleep, of course haste will emerge as a powerful and attractive way to increase overall HPS. That doesn't mean that it'll be the same in Ulduar though. 7-8 minute fights will be common early on, with bosses hitting significantly harder, and raid damage being trivialised by muscle memory much less.
To try and get some perspective on it, what sort of heroic / crafted gear would you wear to do Naxx 10 for the first time, assuming a similarly geared raid? You wouldn't have tanks in full T7 and DPS laughing all the way through 6-7k Patchwerk parses. If you stacked haste in that situation, back when Patchwerk lasted 4-5 minutes, then you'd be in trouble. Sure, it'd probably still be doable, but it'd be a hard slog, much harder than necessary.
My reasoning for choosing Int on my gear is simple -- it's the best stat to stack for unknown / progression content. It gives me a much larger mana pool to work with, and more margin for error (and error will always occur when learning encounters). It's the same reason tanks should be stacking EH while learning fights. Once you're comfortable with the mechanics of the encounter and the specific sort of healing that it will require, then you can begin fine-tuning your gear. In many cases this will mean sticking with Int, in others it will mean switching to a much heavier, output-focused set, or even intentionally dropping haste for _more_ regen (even if it is MP5). The key is knowing when to do this. You coming here and saying that you don't understand why Paladins need 25k mana pools suggests that perhaps you still have some learning to do about your own class.