Enliven is a javascript plugin (with a very small php page) to add functionality to user generated content, by including the file and calling the function on page load it enhances any mentions of twitter names.
To demonstrate, if I mention my twitter name @james_lelyveld here, the script recognises (assuming you've got Javascript enabled), and you can click on the username to see my last 5 tweets.
The functionality is independant of content, the user entering the copy doesn't need to add any special markup, I only have to mention @psd for example and it'll pick it up. Where as it shouldn't pick up john_smith@yahoo.com or testMail@lelyveld.com, however if I mention @philhawksworth...
The idea is to expand this to pick up more options (flikr, last fm etc) and allow easy configuration. The code is open source & available here.