Misery, my go-to shadow priest, has some good insight on the change, and says that sure, if shadow priest DPS was too high, it was too high. But it's too bad that Shadow Word: Pain had to take the nerf, especially since you get it so early on in the class and it's such an iconic spell for the spec. The reason these guys are so happy about the hasted DoTs is that DoTs as cast don't really scale with your gear -- they just sort of do their damage on their own. When haste got put into the equation, shadow priests became happy that they could go after more haste to increase the DoT part of the damage. They could tailor the spec and spells the way they wanted to use them.
Patch 3.3 is the last major patch of Wrath of the Lich King. With the new Icecrown Citadel 5-man dungeons and 10/25-man raid arriving soon, patch 3.3 will deal the final blow to Arthas. WoW.com's Guide to Patch 3.3 will keep you updated with all the latest patch news.