The information on this page should help themers style the Facebook-style Statuses module.
Styling an individual status update
Most of the time you will see status updates in Views. To style status updates in Views you can usually just edit the view to provide the fields you want (although the defaults will work for most people) and then use CSS to add whatever styles you need. If you need to do something more advanced, you can override the Views theme templates.
To theme individual status updates not in Views (for example on
example.com/statuses/SID) you can override
facebook-status-item.tpl.php. Copy this file to your theme's directory, edit it as desired, and then refresh your theme registry cache. You can learn more about theming for Drupal at Overriding theme-able output in the Drupal handbook.
facebook-status-item.tpl.php has documentation in it that explains what variables will be available to you for display. (Of course, if you only want to make simple changes, you can usually just do it in your theme's CSS file.)