Su.pr connects directly to your twitter & facebook account allowing you to tweet or update your Facebook status within their own interface, the good part about this is that it also allows you to schedule tweets or status messages to go out at a later time.
Once you have send out a tweet, su.pr will track and create detailed analytics for the post, in addition to promoting the link to SU users. You will also able to see the the number of views that you received from Stumble upon users, the number of retweets and so on.
In addition to that Su.pr also allows you to create Short URLs on your own domain and provides WordPress users with a plugin to integrate Su.pr into their blog and a handy bookmarklet to shorten URLs from anywhere.
Su.pr is definitely something you might want to use to get that extra traffic to your server, you don’t need to sign up to Su.pr if you are already a StumbleUpon user.