I don't tend to visit the Google Adsense site much, but its already for quite a while today giving me the message: "The Google AdSense website is temporarily unavailable. Please try back later.
We apologize for any inconvenience."

So i wondered, is the Google Adsense site more often offline or is this a relatively special situation?

AdSense is down for maintenance every 2 weeks, usually on Saturday, between 10am and 2pm PDT.