Nobody posted it publicly yet, so I will. Severe issues for the last four or five hours loading programs, talk-throughs (due to the embedded editor I assume), challenges, and projects.
GDB addressed some of the more technical details in a question as seen here:
Hopefully these issues will be fixed soon. In the meantime, try something you haven't done before on Khan Academy, like the math puzzles available on their YouTube channel, or something new from their science section. Or even take a break from the computer and go outside.