bookmark manager

I’d like to see a better bookmarks manager . One that would detect duplicates ( this is really helpful if you are importing bookmarks from different web browsers ), and maybe even a warning saying you are about to add a bookmark, and do you wish to overwrites it, etc… . I’d also like to easily move, delete, and organize the bookmarks.
I have dabbled with Delicious, Google Bookmarks, etc…, and perhaps a manager that would work well with them would help too.