Delicious is one of the Web's most under-rated services. I've been a heavy Delicious user since 2004 and it's invaluable to me. Not just to store bookmarks but to find stuff I didn't bookmark that I just remembered about.
For example, let's say I remember seeing a site about an awesome new WordPress theme a few weeks ago. I can go to http://del.icio.us/popular/themes and chances are I'll find it. If not, I can go through the tag pages (say, http://delicious.com/tag/wordpress+themes) until I find it. Google does not even compare when it comes to finding content in this way.
Even if I backed up my Delicious account and hosted it myself somehow, it still wouldn't have as much value as it does when combined with 100,000+ other people's links.