There are many fights in which as either caster or melee this is possible. After reading EJ and seeing many unholy DK's pulling over 6k dps in heroics i ran on my tank (some were even undergeared) i was thinking that something like a DK with a 1 button rotation like they can have would be great for such a thing(as they nolonger use SS glyph), as well as things like arcane mages. I don't see many instances where having multiple shaman would be useful for such a thing as their DPS is quite low comparably to other such classes that can have 1 button type DPS rotations (not able to break 7k).
Starting off with a bang on this one. Once again, you're dead wrong. Niley is pulling 10k dps with his Shaman (pre-ICC release).