According to http://superuser.com/questions, there are currently 0 questions on Super User. http://meta.superuser.com/questions says the same about Meta Super User.

The other tabs (featured, unanswered, etc.) are also affected. The main pages (http://superuser.com and http://meta.superuser.com) seems to work most of the time.

Stack Overflow and Meta Stack Overflow are working fine.