Interesting thing about our guild, Primogeniture, raiding post patch 2.4. We again had no problems downing High King Maulgar, Gruul, and Magtheridon all in one attempt. (We did have two tanks die in Gruul, but our druid tank picked it up nicely.) The issue that I found was that there was just too much loot. It took too long. In fact, it took longer to distribute loot than it did to actually kill the boss. (Okay, that's not true, it just seemed that way.) So, I say: NERF THE LOOT!!!
Yes... I'm kidding.
I did pick up one of the three epic gems we got off of Mag. It was a Pyrestone that I had turned into a Reckless Pyrestone. I'm still not 100% sure of the calculations on benefit of spell haste. It would basically be a percent increase in your total damage as opposed to the incremental increase a straight spell damage would have; so it's a little tricky. Haste is going to be much more beneficial if you have high spell damage. It's also different for each spell.
So, for example: It appears that the cut off for Frostbolt (untalented) is somewhere around 1066 spell damage. If you have more than that number, than spell haste is going to be more beneficial to you (as far as DPS is concerned). If you have less, then you should lean towards spell damage. With my spec, with 2 debuffs, Arcane Blast's cut off is around 820. So, see how it can get confusing?
Here's a more solid math example. Leiandra is currently sitting at about 1284 spell damage for arcane and fire (1112 for frost). An increase of 1 Spell Haste on Arcane Blast (no debuffs) should increase DPS by 0.441 where 1 Spell Damage would only be 0.361. Said another way, 1 Spell Haste would be equivolent to 1.22 Spell Damage. So, for me, Spell Haste is better.
Wow... didn't actually start this post thinking I would go in this direction, but I started researching it more and thought it was noteworthy. So, since I got my Vindicator's Pendant of Subjugation last night, that provides an additional 21 Spell Haste. Now I just need another Pyrestone to put there. Where's that Badge vendor? heh.