Search engine optimization (SEO) is something you should be taking into account if you are serious about your CMS. This SEO blog has a nice list of modules/plugins for Drupal, Joomla and Wordpress that help increase your chances with the search engines.
Another Drupal module that is quite useful and not listed is Global Redirect. Search engines do not like it if you have more than one URL pointing to the same content. The Global Redirect module tells Drupal to check for an alias and performs a 301 redirect to the alias name (the one with your keywords in it that should be automatically generated by the pathauto module). This lets the search engine know that you are not trying to cheat by having multiple URLs pointing to the same content.