I never encountered that pixely problem, and I have an ATI card. Though, I never have antialiasing on.
So I just reinstalled Skyrim. The shadows are no longer broken, but my most recent character (a huntress) is broken because random people are attacking me. Time to restart. Again.
I find it odd that reinstalling the game doesn't remove your mods as well. I had hoped it would so I can start fresh with an unmodded game.