Laberbacke: Uh, no? Generally it's just the forums, and for minutes at a time. Right now you can't even start the client in offline mode.
Generally no its not. Its the whole service. As usually once a month on a Tuesday you will get a no connection appear at the bottom and nothing will work, then like today then just like its done this second as typing this the service is back.
Offline mode I cant comment on as I don't use it. But the fact that its back just shows it was just maintence.