Last night, I noticed dozens of reports that Google AdSense publishers were unable to login to their AdSense consoles. The first report came in at 1:59am (EST) from a Google AdSense Help thread.
Most of these publishers noticed a new Google AdSense login page. The page then wouldn't allow them to login. The question is, is Google testing a new login page for AdSense? I know a lot of third party AdSense tracking tools stopped working last night as well. Maybe Google tried to change things up to prevent those scraper bots from bogging down their system? I don't know.
At 5:57 this morning, a Google AdSense representative, William, confirmed the issue and said it was fixed. Some publishers may still have issues logging in, if you do, he recommends "clearing the cache and cookies or try using a different browser."
At about 2:50am, I saw first reports at a DigitalPoint Forums thread that publishers were able to login again. But there are still lingering reports of publishers not being able to login. So make sure to listen to William's suggestion above.