it's down.

from their homepage

UPDATED 16 August, 2007 14:02 GMT: Some of you may be having problems logging in to Skype. Our engineering team has determined that it’s a software issue. We expect this to be resolved within 12 to 24 hours. Meanwhile, you can simply leave your Skype client running and as soon as the issue is resolved, you will be logged in. We apologize for the inconvenience.