In Ubercart > Checkout settings, when you enable "anonymous checkout enabled" it means "checkout without login".

By default, Ubercart always creates a new user during the checkout process, and enabling anonymous checkout just prevents people from having to register and login before they can checkout. Ubercart still creates an account for them.In this case, Ubercart doen't attach the order to the newly created user id.

I think most of the Drupal developers know the Statistics module, which makes part of the Core of D6. It basically logs access statistics for your site. Every time a node is viewed, a counter gets updated. This counter value is stored in the node_counter table, and gets reset each day at 00 AM.

If we want to know, "the most viewed" nodes in the last week, month, etc, etc, ... simply this could be done by setting appropriate Node statistic filter.