The Skype team has made a few statements on the subject, and while they aren't detailing the scope or cause of the issue they are claiming they will have it resolved within the next 24 hours. Skype has stopped downloads of their client software in the meantime, and has suggested to their customers that they simply wait with their client running until it comes back up.
Were Skype just a few months out of the chute, this wouldn't be all that interesting. However, given that they have a fairly ample userbase and that many people have come to rely on VoIP, outages present more of a problem than they did a few years ago. Hopefully, the company will learn from the experience to craft a more robust service.