getdeb.net has been having server issues off and on again. They have been down for about a week now. They have a separate blog on which one can keep up with the situation. All is not lost, though, because according to jedd in the third comment here there is an informal mirror out there. The addresses are:
Add these under System -> Administration -> Software Sources, the OtherSoftware tab, click Add at the bottom of the dialog and paste each of the above lines in as separate additions. The deb-src line is optional and I don’t normally activate third-party source repositories. Click close when you are done and Ubuntu will ask if you want to reload. Click Reload and you’re all set. That will at least keep you going for now.