No.<p>(Personally, I wouldn't try making yet another social bookmarking site. The only way I can see of competing with the existing players is to market it better so that you get users who've never heard of Digg/Reddit/SU/Delicious/etc. Hint: Facebook app, viral features. But I'm not sure how succesful at making money these sites are.)
* Universal (cross-platform, cross-browser) synchronisation.<p>* Tracking my most-searched-then-clicked-on links, and showing them in a "Personal Top 10" stack for quick viewing, which in turn would be its' own bookmark folder.
Full-text search over the pages you've bookmarked. For me, the Firefox address bar (with its rapid search of your browser cache) has made sites like Delicious obsolete. The only webapp I'm aware of that lets you do this is Google Bookmarks (which is asocial).<p>I'm still waiting for someone to bring the pleasure of the Firefox address bar to a social site. I created a webapp that does this last summer (Quocial.com; I can send you an invite if you like, but be warned that I'm no longer maintaining the site), but the technical difficulties of full-text search are such that it really only makes sense for someone like Google or Microsoft/Yahoo to do this. Or, Twitter could start crawling links and letting you run full-text search over either your links or those of the folks you're following (though I'd rather not make each and every one of my links public).<p>In short, the social bookmarking game isn't over yet. I firmly believe that Delicious-style tagging will give way to full-text search. One of these days, someone's going to nail it.
I'd really like to hear joshu's (<a href="http://news.ycombinator.com/user?id=joshu" rel="nofollow">http://news.ycombinator.com/user?id=joshu</a>) take on this.
We have tried to take on the social bookmaking world with out site www.favilous.com - we will take on board all these comments. Some people have said they want to read links later; you can do this using our site. We also introducing a Yammer type service for networks of people to bookmark and share their bookmarks and documents with each other on their network. Thanks for the comments-really helps.
I just installed Read It Later (<a href="http://readitlaterlist.com" rel="nofollow">http://readitlaterlist.com</a>) so I can bookmark links which are interesting tweets to my followers. They have an API, which could be used to automate some of the work needed to prepare the tweets.
The field is still so new you are better off actually implementing some features you think are missing rather than taking surveys about them. Nobody really thought anything was missing when del.icio.us started, either.
The only issue I find is that the popularity of such sites seems to be inversely proportional to the amount of interesting content in there. IMHO, Pinboard (pinboard.in) solves this problem quite nicely.
I think the answer is in why so many people are enjoying Instapaper. My problem with delicious is that it's too hard to get links in to the damn thing.