Given the culture of hacktivism that is evolving on the Internet, my first thought was that perhaps Skype is the victim of some sort of denial of service (DoS) attack as a backlash for shunning the open source community with the decision to pull the plug on support for Asterisk. Sony, and companies that worked against Wikileaks know all too well that hacktivists can be a force to be reckoned with.
There are many users on the Internet blaming the outage on...wait for it--Microsoft. I am not sure if the conspiracy theory is that Microsoft is somehow directly responsible for the outage, or if the tinfoil hats just think that Microsoft's intended acquisition of Skype has drawn the ire of anti-Microsoft hackers. Either way, Microsoft doesn't own Skype yet, doesn't control Skype operations, and doesn't pull any strings at Skype, so the Microsoft-bashing angle is silly.
As it turns out, though, the outage appears to be much smaller than suggested, and not as nefarious as I had assumed. A Skype blog post explains, "A small number of you may have had problems signing in to Skype. This predominantly affects people using Skype for Windows. We have identified the problem and will issue a fix in the next few hours."
As the blog post states, Skype is working pushing out a fix, but in the meantime, Skype provides instructions in the blog post for Windows, Mac OS X, and Linux users to manually resolve the issue and get re-connected with Skype. For Windows users, the instructions amount to shutting down Skype, removing an XML file called "shared", and restarting Skype.
For most affected users, this is little more than an inconvenience. But, there are some businesses that rely on Skype as a primary means of communication (hence the backlash over dropping support for Asterisk). Many businesses also use Skype as a means of cost-effective video conferencing.
The Skype outage illustrates one of the primary challenges of relying on cloud-based services--sometimes the cloud isn't there.