Google launched their own online URL shortening tool some time ago, we have been using it for the past year.
They have now developed it with a fancy bit of code that shows how many clicks your particular shortened URL has had. For example, I Tweeted yesterday and included a link to this page http://www.arkom.co.uk/news/article/google-updates.asp which is far too long for Twitter so I shortened it to http://goo.gl/1akd9 using the shortening tool
Now when I go back on I can see that 9 people have clicked on that link in the past 2 days. A nice touch by Google allowing to track the effectiveness of your links whilst going about your daily marketing!