Are shamans really useful in groups and raids?

[username17]

They're excellent in groups. After I have everyone buffed (if I'm not healing or hasting) I'll pop out my 55 pet and toss a few nukes as well.
On raids they're needed but you only really need one Shaman. And you'll be a buff bot on raids 99% of the time. Slow is very helpful if the boss is slowable though.

I would NEVER use Shaman and mediocre in the same sentence. They are far from it.