Really, how difficult is it to have a site and service that stores links and tags? Even at a high volume of data, in this day and age it should be trivial unless the money's not there to support it.
According to http://blog.delicious.com/ , they cancelled the premium service in January, attempted to monetize it again via sponsored links in RSS feeds in March, failed to revise the site successfully in March, then had "site problems", and finally said this month that they would be transitioning back to del.icio.us, but they seem to have been unable to do that either. Now the site's either down or stating that it has too much traffic. They've completely screwed the pooch.
It's really sad.