Skype going on right this minute, judging by the explosion of tweets relating to it. It's not universal, as we've been able to log in and use the internet communicator for both text and video chat, but something's definitely gone wrong. So far, we've noticed our OS X machines are ticking along just fine, but our Windows computers are not. Importantly, we had to upgrade one of our Windows desktops to "break" Skype, which indicates it could be a fault contained in the latest version, but then again, it could have simply been just a case of terrible timing. The iPhone and Android apps look to be unaffected, but skype.com is down and out. Skype is on the case right now and will have more details for us "soon."
Update: Skype has a solution for bringing tech savvy users back online. It requires deleting the shared.xml file, instructions for which are available for Windows 7, XP and Mac OS X (so yes, Apple computers have been bitten by the same bug too). A simpler fix is said to be in the works as well.
Update 2: Looks like Skype is back to normal now. Phew!
Update 3: If you're still experiencing issues, a Windows software update is now out and a Mac update will follow tomorrow.