I use it to bookmark anything that I might find interesting enough to revisit someday. In that way, it’s great for collecting programming reference/techniques or for tracking political discussion or even just keeping tabs on cool bits of design I stumble across. In doing so, I have to make liberal use of tags in order to find anything in the future.
I do not use it to bookmark sites I heavily visit. That’s what my browser’s bookmarks are for.
I’m also playing around with Mento which has a couple of nifty features:
– ability to associate a picture with the link in your bookmark stream
– auto-propagate Mento bookmarks into delicious
And I’m considering Ma.gnolia. While it can import all of your delicious bookmarks, it lacks some of the Mento features. Not sure yet if Ma.gnolia has enough differentiating factors to pull me off either delicious or Mento, though.