But TWF is already quite severely disadvantaged in that (1) it needs a special feat to overcome some of its massive penalties, and (2) it can only be used in a full round attack.
I don't see it being especially useful for a character other than a rogue, and if it weren't for the rogue's potential sneak attack bonuses, it wouldn't be a huge benefit to him/her either. Consider: the only way a rogue can get into position to use TWF is to be within 5 feet of his target at the start of the round, and to get the sneak attack bonus he needs either to have surprise or to be flanking his target. How likely is that?
So, given the right conditions, a rogue has the potential to do a LOT of damage, but the conditions needed are quite restricted.