Thanks for the detailed review! It's useful for us to hear all of this feedback. :) Just a couple things to note: you can suggest bookmarks to other users by tagging them with for:[username], and we're thinking about more social functionality (this related but semi-old post might be interesting to you). Also, Delicious has some advertising, for example on the right side of search results pages, but it's clearly marked; there's definitely no paid placement on the hotlist.