Roland Delacroix said:
Celerity is overrated. Lets say a typical cleric takes it. I've never seen a cleric in Light armor, so the movement bonus is negated. The Init bonus is nice, its worth less than half what Time domain gives, a single feat Imp Init. The other good ability, Enhancement +2 Dex, is pretty good.
Only two deities grant access to the Time domain, one of which can only be worshipped by elves. And not all DMs allow FR content.
The Dexterity bonus also adds to initiative. So the Celerity domain gives you +3 to initiative. Plus, the initiative bonus from Celerity stacks with Improved Initiative. So take both Time and Celerity, and get a total of +7 to initiative.
Celerity and Time also give you Haste and Mass Haste as domain spells. A cleric with the Travel and Trickery domains, who takes 1 level of Contemplative and chooses the Celerity Prestige Domain is practically a wizard, in some respects. He can Fly, Haste himself and others, Teleport, cast Invisibility, use Dimension Door, and cast Time Stop. This is in addition to all of the normal cleric spells. It's not that the domain is overpowered for every character. But it can be easily abused to get lots of extra power.
As for those 2 PrCs...
The Sacred Exorcist gets everything a normal cleric gets, and then some. He continues with full spellcasting progression, as well as full Turning progression. The BAB progression is the same, as is the Will save progression. So a cleric gives up a good Fortitude save progression in exchange for a ton of new abilities, including a Prestige Domain, 3 Extra Turning feats, and a permanent Consecrate spell. The 3 free Extra Turning feats are even more powerful when combined with Divine feats, which use up turning attempts.
The Templar, on the other hand, isn't overpowered (most of the time), but it is front-loaded. Just one level gets you Weapon Specialization and Mettle, which are two very nice abilities. IIRC, it's the only Prestige Class that gets Mettle. And Mettle can be easily abused when combined with someone who has Evasion and high overall saves (like a Monk, a Paladin/Rogue, or a Cleric/Monk or Cleric/Rogue with the Mysticisim Prestige Domain).
Take a Templar of Illmater, for example. You now have a Monk who has both Evasion and Mettle, Weapon Specialization (unarmed), Damage Reduction, and spells. Plus, after they are done with the Templar levels, they can get even more power through the Sacred Fist PrC.
And the Contemplative is front-loaded, too. Most of the people take it for just one or two levels, in order to get a Prestige Domain.
But despite how it seems... I like DotF.

I was merely trying to point out to reapersaurus how lots of other things, besides the Hospitaler and Armor of Speed, can be unbalancing. Hey, I could probably do the same thing for every other book out there.