I am always wary of tools that try to combine metrics with social media, like Twitter Grader and Twitter Follower Friend Ratio. The main reason for this is the risk that people who don't understand the nature of social media (engagement, conversation and a way to make being genuine a real part of business and personal online interaction) will use the metrics they attain to spam or abuse those in the social media space. Also, turning it into a competition defeats the whole concept of microsharing.
BudURL seems to have found the right mix of metric and social by keeping it simple. Unlike Bit.ly with its custom keywords or TinyUrl with its custom URL feature, BudURL gives you a way to track where your link was clicked. Keywords take time to track and rely on third party software for adequate information, and custom URLs are handy for sharing a link but offer no tracking. To see your referrers without any keywords involved is useful.
The lack of a keyword metric also helps prevent certain kinds of spamming. There is a huge subset of people and businesses out there who watch keywords like a hawk, looking for any opportunity to "game" a system with keyword metrics. By concentrating on where your link was seen and not the keywords around it, you are getting useful information and not contributing directly to a potential spam issue.
My favorite part of BudURL is the real time aspect of the referrer list - it auto refreshes every few seconds as people stop by your page. It was fascinating to me to see the test link I tossed up on Twitter get sent around the Internet. I got a fair share from Twitter, but I also got to see when someone else picked up the link and put it on other sites.
For people concerned with privacy, they may take issue with BudURL's tracking of visiting IPs. In addition to referring URLs showing on the list, the visitor's IP is tracked as well. I love this feature - I have a burning desire to see where my readers live and work. I find it interesting. However, if you are nervous when people know too much about you, it may help to keep in mind that clicking on a BudURL will give the person who made the URL your IP.
BudURL also gives you a way to track your BudURLs and create notes to help you remember what they were for. It also offers a toolbar button you can use to easily create BudURLs. Just add it to your toolbar with a simple drag and drop and click it when you are on a page you want to make into a BudURL. It took less than a minute to sign up for the service and install the button for me, and I didn't even have to wait for a confirmation email. My account was active right away. Additionally, my URL tracking was active from the moment I first sent the URL out into the Twitterverse. Instant gratification is always a winner for me with a new application.