"UPDATE #1: Bethesda informs us that the content has not been removed; there is simply a lot of traffic at the moment causing the content to become unavailable. We will update when things cool down. The original article is as follows.
Today, fans of Skyrim around the world have rejoiced: Bethesda has officially, at long last, released the Creation Kit, the official mod tools for the community to take full advantage of the game and create crazy custom content.
The mods themselves can be easily located via a nifty new place on Steam called the Workshop. Players can find a mod, easily install it, subscribe to the author, write recommendations, et cetera.
Do you remember the zany Space Core from Portal 2's ending?
A rather mysterious companion mod appeared, and was almost immediately removed."
Update #2 - The initial stress on the servers has been alleviated, and you should be able to download it easily. Link is in the article.