From everything I have read it isn't against the ToS. In any way shape or form. You can even brag about using it ( derbie being banned ( or whatever his name ) was very wrong ( but notice they banned him from the forums not the game )). ACT does not do any form of data mining. What ACT does is take the text from the combat log and add up the damage then divide that damage by the amount of time you were in combat. If its bannable then SE needs to rework their tos because there is nothing stopping someone like me, RAIN MANISH who can add up numbers very quickly in my head as they scroll across the combat log, much like act. Guess I should be banned as a player.

However it is against the ToS to use that information to harass someone

I.E. You dps sucks, get a life = not okay
I.E. Hey man you did a great job dps = okay
I.E. Vote kick someone out of an instance because their dps is low = ok
I.E. You fucking suck then kicking them = not ok.