Collaborative Rank is an experimental service based on Del.icio.us. It allows to see the ranking of users (I an at 5168). I am not sure how the ranking is determined. It seems to be that the first one to bookmark something, which is subsequently followed by others gets a higher ranking. Also interesting is that an area of expertise is determined bases on tags used. For me it is the tags: tags, tagging, bookmarks, web2.0 and social. Sounds a bit strange collection to me. If you search for a tag, you can see the corresponding bookmarks and the tagging sequences, i.e. the users that tagged that bookmark in sequence.