If you were already signed in this morning, stay that way. But if you had to reboot you computer last night like me, then you might not be able to get back in. They are reporting the status here: http://heartbeat.skype.com/2010/12/problems_signing_in_to_skype.html
But even though it says all is well as of 12:20 CST I'm still not able to sign in. You just don't realize how much you need something till it's gone. Now I have to rely on the phone, or email, or twitter, or my blog, or facebook to communicate...it's like the dark ages..or google talk (but I stopped using that a long time ago). Truth is, Skype has become a mission critical tool for our company and has so few problems (other than a slow decent into unusability with each interface iteration - especially on the Mac).
Get it together guys. 
Update (12:30pm): I forget sometimes that Skype is a peer-to-peer network. Apparently an update to the software took out some of the "super-nodes" (users that are online a lot - heck, I might be one of them). When those nodes failed, the network came down, at least for me.. http://blogs.skype.com/en/2010/12/skype_downtime_today.html?cm_mmc=PXTW|0700_B6-_-downtime-20101222
Update 2 (6:34pm) : A full day of yelling a Skype on Twitter yielded nothing but some mild comic relief. If you enjoyed this post - you'll really like my twitter diatribe: http://twitter.com/#!/benshoemate