Waleed asked something similar recently.

See this thread for some ideas : http://news.ycombinator.com/item?id=31244

I think he posted a summary of sorts here http://selfdebugging.com/

Perhaps you should ping him and see if you can join up ;-)

The first suggestion that comes to mind is to automate as much of the process as possible. I rarely use social bookmarking sites because, 1) they waste more time than they save, and 2) I don't have the patience to sort through the details of URL submission.

See if you can develop a heuristic to determine a user's favorite sites based on their browsing patterns. Convolve that into a set of browser extensions and expose the user data through a web front-end. Make personalized suggestions based on user history. Auto-generate site summaries by looking at page markup (size of fonts, page title), that sort of thing.

CoReap is one service that I've started using more frequently off-late. It combines social search and social bookmarking with a no-frills browser sidebar for bookmarks management and a browser extension for social search integration. See: http://www.coreap.com

One word: community.

Just don't forget the users who could care less about the community and just want a place to put save bookmarks. Google Bookmarks is good for this, but I like to categorize my bookmarks in bulk and Google does not work well for this.

Thats a given... I was wondering along the lines of technical features.

Well, you have to enable a community through the technical features, is the thing. The community has to be intrinsic in the tech.