I was browsing the blogsphere and came across http://www.BlueDot.us. It is a social bookmarking site with a lot of AJAX and the ability to have links, representative thumbnails from the bookmarked page and ofcourse – tagging.
When I hit the site, it was a bit slow, but that is understandable given that they really were not ready for the kind of attention (they mentioned on their blog.) Good luck to them, hope they find what they are looking to achieve with the site.
Reminds me of 1999-2000, the entrepreneurial sprit never fails.