I swear in teh patch notes, they said TC got a SLIGHT, as in almost unnoticeable nerf.
Thunderclap: This ability was left at 10% despite the haste effect changes. This means its potency has been reduced slightly.
http://www.worldofwarcraft.com/patch...atchnotes.html
I think somebody calculated it like 9.8 or something instead of a perfect 10%. It almost made no difference at all.
And in regards to your first question, I don't really understand what you're asking. Imp thunderclap is only rage reduction. Are you talking about the BC TC or Conq. bonus?
http://thottbot.com/?sp=11581
Thunder Clap is a 10% speed reduction.
and for #2, TC is physical dmg, so it won't work on Vek (twin emp). I don't think there are any other physical dmg immune mobs. to sum it up, i think works on all but one boss.