Actually, only one priest, and he's sort of a tool. Pawne of Box Lunch on Dentarg says he'll never heal a shadow priest, and in fact refuses to group with them at all, which must make raids interesting. If the group he's in has a shadow priest, he makes the group kick them before he joins. As expected, all the other priests (shadow, holy and discipline) tear him apart for defying priest unity, having bad gear, not being 70, and pretty much anything else they can get their hands on. The Armory really makes making fun of people on the forums a lot easier.
The argument then descends into hilarity as the priests call him a bigot and he calls them nerds, as if arguing on a WoW forum didn't make everyone involved a nerd. Since Pawne has also posted that he doesn't like turning into a girl when he dies, I suspect he's either a clever troll or not exactly at the front of the line when brains were handed out.
I understand why some guilds don't like having all shadow priests -- you do probably need the majority of your healers to be healing specced if you want to be on the cutting edge of new content. Nevertheless, as a rogue, I love being grouped with a shadow priest, since vampiric embrace heals us when everyone else seems to have forgotten us. If I ever stop being lazy and level my blood elf priest, she'll be shadow until 70.
What do you think about shadow priests?