I’ve always been an avid user of delicious for my bookmarks. I love the way I can just type away on tags, without having to worry about cataloguing my bookmarks in hierarchical folders. Moreover, my bookmarks are stored online, so as long as there are no Ma.gnolia-like debacles, I can access them from wherever I want. This alone makes me prefer Delicious over any browser’s built-in solution.
Anything you put in the bookmarks bar, you can access with cmd + the place of the bookmark in the bar (from the left). This means ⌘1 opens the first bookmark, ⌘2 the second and so on. Combine this with bookmarklets and you have keyboard shortcuts for things like adding a delicious bookmark without any third party apps. As you can see, I also use this for other services that provide bookmarklets, such as Evernote.