The way I discovered SF was down was when I was trying to install some Slackbuilds and kept getting MD5 mismatches on the source downloads. I noticed I was getting the same MD5 for several different packages, so I tried to manually grab a package and that's when I hit SF's error page (which sbopkg was happily downloading and trying to pass off as somesourcepkg.tar.gz).

I found myself in the odd position of hoping SF would come back up so I could finish what I was doing, when I'd normally welcome the news that they had shut down.