Twitter seems to have replaced social bookmarking services. Perhaps its just within the admittedly small community that I follow on occasion, but it seems to me that the main reason for a very large percentage of tweets is simply to share a link with a brief comment. While putatively for personal information management, a major reason that people use social bookmarking services (like Del.icio.us, Connotea and so forth) is to share (hence the 'social')  and I frankly think they do a better job of it then the ambiguous tinyurls and bit.ly's taking up valuable character space in tweets.
But... Connotea and its brethren are the past and Twitter is the now so here is a suggestion for making the twitter of tomorrow a tiny twit better. Perhaps it should be possible to simply make the entire text of a tweet a link. Same function, more visually appealing interface and more characters left at your disposal.
Just a thought.
 In my own experience sharing has really become the primary function, with refinding old bookmarks almost always easier with a new Google search then via my own tags (even my fancy tags).