Jez,

I don't like to step on Ryan's toes but I have an answer for you.

For us it depends on the client, for budget projects we just do a CCK Field or two related to featured products and use views to display a block and a page.

For jobs that require it we use the Statistics functionality built into Drupal core. You can read a little on it here http://drupal.org/handbook/modules/statistics. I have also used the Drupal Hall of Fame module located here http://drupal.org/project/hof.

Both require some customization and theming to work exactly how you would want them to work.