Tweetbacks is in beta (not to be confused with Tweetbacks the other site) at the time of this writing. The creator explains it like this:
They work kind of like trackbacks, but instead of listing blogs linking to a specific post, it lists Tweets about a specific post. It currently finds mentions of the URL through the top 5 most popular URL shorteners on Twitter: Tinyurl, Bit.ly, Is.gd, Twurl, and SnipURL
A great way to show off people sharing your content and allowing readers to find other Twitterers that may share a common interest also. Dan also has other Twitter tools that we have highlited like Retweet Mapper which follows along the idea of this tool.