I'll join my voice to those that dislike doubleweapons.
To tell the truth, I loath them. Allowing silly fantasy weapon that defy physics is fine, some people like them. But making them super-Superior weapons, why?
To be fair, they are only completely out of wack for two case; Rogues and Tempest.
For a ranger, they only grant +1 to AC and the advantage of not needing two different weapon to keep pace in the magic item rat race. Probably a better deal than using two bastard sword IMO (also an eyebrow raising concept but at least one that is balanced) but not terribly unbalanced.
For a rogue; doublesword make Rapier obsolete! Why on earth would a rogue pick a rapier when a doublesword gives the same attack bonuses and damage but also give a +1 to AC! The idea that any min-maxer worth his salt seeking to increase his damage dice will bypass the rapier, a typical rogue weapon, and go for the doublesword makes me sick.
And the tempest ; Just forget it. What they seem to be trading in for their build is completely recuperated by using the doubleweapon. A tempest using two short sword seems balanced, one using a doubleweapon seems highly suspicious to me. At any rate, that one feat gives him a ludicrous boost in power!
I keep expecting some errata, but nothing yet has come down the pipe. I hope it's coming, they have errataed some much less problematic stuff.
My personal solution is removing the off-hand tag on the doubleweapon and the light blade tag on the doublesword. The weapon is still silly, but roughly balanced IMO without these feature.