I've written before about the use of URL shortening websites with Twitter and while I had been partial to using tr.im, I've made the switch over to su.pr and here's why:
su.pr allows you to not only shorten a URL for one of your blog posts, but you can also post to your Twitter and Facebook accounts as well as bookmark your blog post to StumbleUpon
If you are interested in effectively marketing your blog posts or any of your other items, then you need to consider all the different ways you can publicize their posts. And it becomes tedious to try and update or post to each site individually - this is how combination sites like su.pr can help. You will need to set up a StumbleUpon account and then link your Twitter and Facebook accounts in order to reap the time-saving rewards of su.pr.