I popped over to Twitter a few minutes ago to do a little more exploration. I was going to set up my cell phone to handle sending and recieving messages to the service. I was greeted with no CSS.

I think I'll wait to navigate the site. However, this is an interesting illustration of HOW important layout/graphics are to usability. All the functionality of Twitter sits intact, but the page has become difficult to use because we can't see where the elements lie easily.