If you use Google Analytics to track your website traffic you should read this. Google Analytics now provides a new Asynchronous Tracking Code snippet as an alternate way to track your website.
Think of the asynchronous tracking code snippet as a script that uses a "separate lane" to handle part of the processing of your webpage. As the number of cars (or in this case, scripts on your webpage) increases, the asynchronous tracker uses this lane to reduce webpage load time. Websites that use many scripts or rely on rich media content will especially benefit from this new method, but even lightweight sites will see improvements.