Just a note. Last night I MT'd for 25 man Arch and had a very hard time getting aggro back after getting tossed. I would jump back in the fight being 2nd or 3rd down in aggro and hit taunt (followed by SS, Rev, and Dev etc. etc.) and watch my aggro on Omen not budge. I had to wait through 2 cycles of taunt to get aggro back. This happened consistently throughout the fight. It seemed that taunt was not setting me equal to the highest threat, basically it seemed that taunt was not working at all.
I have tanked 25 man Arch before and not had this issue of taunting and nothing happening.