Now it's working again after letting it sit for a while - must be a backend server issue.
Yeah, something seems to be wrong. I updated to the latest version of OS X Mountain Lion and the latest version of Evernote desktop (Version 5.2.1 (401587)) and when I try to login to the desktop client I get the error: Please check your internet connection or try again later. I can login via the web client on Safari just fine. I've even reset my password but the desktop client still fails with the same error above.