replicant2 said:
That was my impression as well, though our DM interpreted the rule as just the primary attack. I hope to convince him otherwise, but let me ask: Do you think sneak attack damage with two weapons is unbalancing?
Yeah, your DM was in error. Hopefully you can convince him of the right way to interpret these rules.
As for whether or not it's balanced, it is.
In order to gain a large number of attacks with a large sneak attack bonus, you need:
1. A significant chain of feats (TWF, ITWF, GTWF, PTWF) with significant prereqs
2. A large number of rogue levels
Together, those mean that you'll have, generally speaking, few feats to put into other character abilities and poor survivability. In other words, you'll be remarkably specialized in doing one thing very well, but you won't have the AC or HP to stand up to most bruiser monsters' full attacks.
There's also a large number of foes who won't be fazed by your sneak attacks at all: undead, oozes, elementals, constructs, etc.
Taken together, full sneak attacks on multiple-weapon fighting is balanced.