If you're like me and currently unable to log in, hold off for another day and try again. It seems that their behind-the-scenes upgrade of a key database is taking them longer than expected.
I'm simply getting declined access when trying to log in with the desktop client. However, when trying to log in using a web browser I see this message: "We're migrating users to the new version of Producteev, if you're not able to log in, that means that your account hasn't been migrated yet. Please bear with us." This is 'backed up' by the current raft of comments in their twitter account.
So, I'll reserve judgment for now... :-)