I don't think any of the bonuses or abilities in the dual wield tree work as intended. I'm also not convinced that your "Swords" specialization stats are supposed to double when you wield two swords, either, but I don't think there's been official word on that.
Offensive Maneuvering works, but none of the +counter passives in the tree work. I don't know about the doubling of sword spec points, but then again I haven't paid attention. Unless I'm playing a mage build, I pretty much always have dw.
the passive don't work, however 'activated buffs' work, aka offensive, equipping two weapons gets the skill passives for each tree or double if the same type if you wield two swords you get double the tree now in 1.03, or mace, or etc
Thanks a lot, guys, that's really helpful. Guess I'll learn that skill in my next run. I haven't been able to not use Dual Wielding since I learned how powerful it is. Can't see myself with a non-Wizard character that doesn't have this, and Vampirism.