I read an article somewhere that they are having hardware problems on their web server. The FTP and other portions of slackware should be up from what the article said.
I had been curious about this as well. I do hope they get everything up and running as soon as possible. I do not visit the site that often, but it appears they had trouble with the site being down for a few days back in April as well. It definitely sounds like they need a host change as soon as possible. I think Rob's recommendation is a great idea!