Also, I want a bookmarking system with some smarts, i.e. that can categorize bookmarks itself. And of course I want to be able to search that, including any tags that I might have attached to a page. Think of del.icio.us, but without the privacy horrors.
After all, we often take a very strange path from one place to another on the Web, and the challenge of properly categorizing bookmarks makes it easy to skip doing it at all, especially since it's hard to sometimes remember where you put a bookmark.
Some people have a great ambition: to build something that will last, at least until they've finished building it.