URLs are extremely important and the ability to be as informative as possible with those URLs is equally important to us. Gists are now namespaced in much the same way that repositories on GitHub.com are.
Previously, Gist URLs would look like this:
Now, they look like this:
URLs in the old format will automatically be redirected to their namespaced equivalent. Finally, a bonus moment of zen! It'll be a lot easier to find your gists in the wild.