The era of Icecrown Citadel was a strange time for enhancement shaman. After spending 2/3 of the expansion gemming primarily attack power, haste rating became our king. I still remember the odd whispers I got from concerned guild members as they saw all yellow gems lighting up my gear, and how my go-to jewelcrafter was always certain to ask "are you sure" every time I asked him to cut a Quick King's Amber.
The enhancement of ICC breathed haste. It sped up our white attacks, which in turn increased Flametongue procs, Static Shock procs, and the then all-important Maelstrom Weapon procs. This wasn't necessarily a good thing, because nearly every other melee at the time was scaling with armor penetration, a non-linearly scaling stat that absolutely murdered its victims. While other melee classes and hunters saw their damage climb steeply, the graph of enhancement shaman's damage plodded on in a straight line.
Cataclysm brought about a change for enhancement shaman and their old wingman, haste rating. With Maelstrom Weapon being lowered in the priority list, Static Shock being tied into our weapon abilities, and having our actual abilities hit for more damage, haste rating went from being our best friend to our worst enemy. It's like high school, but for stat ratings.
To understand why haste is so bad for us now, it's necessary to first understand what makes it so good for other classes. Up first, HOT and DOT classes.