Very weak. I wanted so badly to be a dual dagger, but the point of dual wielding is to use power attacks. It is impossible to dodge, move in to power attack, and dodge the next because of the delay. I was forced to switch to swords and fared much better.
On the other hand, I refused to use enchanted weapons. And I can switch back to daggers now that my Alchemy is 98 and poisons are strong.
I've been using Dual Daggers exclusively myself. It takes a lot more finesse than the other weapons, you get used to dancing around a lot to dodge attacks. Using Light armor also helps. You generally want to combine it with Stealth attacks, and the perks that increase sneak damage.
I wanted to mess with Crafting because you can do some insane things, for my after game, so thats why all of the Crafting perks
http://www.ign.com/builds/the-elder-scrolls-5-skyrim?d=000000000000000000000000000000000000000000000000000000000000000000000000000000000051111111111111111110000000000000000000000000050100000215111123115100010005111115111111110000000000011000001