Haste doesn't help the start of the spell, only the /recast - that's checked at the end of the spell. I'll try to explain.
Fast Cast - If you have this on, the spell should go off sooner.
Cure Clog - If you have this on, the spell should go off sooner (matters only if it's a Cure).
Haste - If you have this on, it does nothing.
Light/Dark Arts - If you have this on, the spell goes off sooner/later based on if you use the right type of spell.
Fast Cast - If you have this on, the /recast timer should be shorter.
Cure Clog - If you have this on, it does nothing (doesn't matter if it's a Cure).
Haste - If you have this on, /recast timer should be shorter.
MND, Enmity Down, Conserve MP, Cure Potency, etc - Benefits like these kick in if you finish the spell with them on.
When you start a spell, there is that little bar at the top that shows you are casting it. At some point, your spell goes off. If you have no Fast Cast or Cure Clogs or Cure Speed merits or Light/Dark arts, then that bar has to fill all the way to 100% before it goes off. If you have something that makes you cast faster, then the spell goes off before 100%. The faster you are, the sooner it goes off. Notice I didn't mention Haste because Haste doesn't make you cast faster.
The Casting Speed bonuses work on a tiered system. What that means is that if you make yourself faster, your spell fires off faster only if it breaks a certain speed threshold. For the purposes of WHM, all we need to care about are two tiers in specific:
1) Cure Clogs + Light Arts + Cure speed Merits x 2 = Highest Tier (/sch sub)
2) Cure Clogs + Cure speed Merits x 5 = Highest Tier (no /sch sub)
If you routinely go /sch, you can therefore put merely 2 merits into Cure speed and not 5, freeing up 3 more to optimize other aspects of your job.
When you open your menu and see your spell greyed out because it's not ready to cast again, you are waiting on your /recast. You want that delay to be very short so that your spell goes white as soon as possible so that it's ready again. This is what Haste affects. Fast Cast also affects this because Fast cast affects everything. Cure Clogs don't affect this.
Since Cure Clogs affect the start of the spell, and Haste affects the end of the spell, you should start Cures with clogs on, and finish them with Haste (blessed) on (also, the -enmity and MND benefits).
Stats like MND, -enmity, Conserve MP, Cure Potency, etc, all check at the END of the spell, not the start. Finish casting with these stats on when you can. As a result, you should start casting buffs in Rostrum Pumps, and finish casting in Blessed. The reason we don't finish the cast in Rostrum Pumps, even though it has Fast Cast (and that helps at the start and the end), is that Blessed's Haste is also going to help at the end, and in addition to that Haste, Blessed has -enmity, giving you a double-bonus.
EDIT: To the poster above, if you use the new pants for Cure Potency and movement speed, for example, then you have to choose between:
End spell in +Potency
End spell in Blessed (Haste, MND, -enmity)
You see now why it's problematic. You can't end the spell with 2 pairs of pants on.
Edited, Nov 1st 2009 5:48pm by NatePrawdzik