When to stop gathering haste?

[Hachoo]

haste rating doesn't do much for mages (as opposed to crit for example which rocks for mages)

for shamans haste or crit, it doesn't matter, both add roughly the same dps. The difference is, with haste you'll end up getting diminishing results, whereas with crit you do not. (Don't think it's possible to hit the crit cap with gear. :P )

I'm unaware of when haste gets diminished, but i reckon I sit fine at 250ish on my chars.

Thats true...sort of. Depends on how you look at it. Technically going from 20% crit to 40% crit does absolutely nothing for Lava Burst, so I would consider that quite a large diminishing return, but its all in how you look at it Still, I definitely want to know where it stops becoming effective to stack haste so I can avoid it at that point.