Debuffs in raids

A question for the instance raid veterans out there: What debuffs do
you consider to be mandatory?

Last night in MC we had four mages and five warlocks, but nary a Curse
of Elements to be seen on any mob or boss all night. I even asked a few
of each class whether we should be using that, and indifference was the
general reaction. I wonder if it's just ignorance, or other curses
(e.g. Agony) seem to produce better results, or if these folks are just
thinking of their own position on the damage meters and don't want to
waste time/mana on debuffs that help others.

Also, Thunderclap seems like an amazing nerf -- 10% attack speed
reduction which should reduce physical damage (and casting as well?) by
10% against the MT. Does anyone have better knowledge of this? I
haven't found a boss that is ever immune to it. When I'm a standby tank
or just dps warrior in Battle Stance, I make sure to maintain this
debuff as well as Demoralizing Shout (small dps nerf but every bit
should help) but I seem to be the only warrior bothering with it.
.