Visitor source capture has been improved in V2.4. If you use Google Analytics to track your site trafic, this matches with GA to capture visitor source without any configuration. When visitor registers or places order, the source will be automatically recorded. You can then run report tool to show metrics.
In the user tracking and who's online reports, you will see the visitor source, medium, keyword, campaign etc. See below for the snaphsot.
After visitor places the order, the source will be stored as well.