Do non-enabled modules affect performance? Does having Drupal modules present, but not enabled have any effect on the performance of a Drupal site?

To put it another way, would removing disabled modules on a Drupal site have a positive affect on performance?
Generally no it will not affect performance - except for when you are viewing your Modules selection page (admin/build/modules or admin/modules). Disabled modules are not loaded into memory and never executed.