I was checking Google rankings for an audiobook store. This site is also the root for a number of sites running under it in a multi-site environment. I was looking to see how a particular page fared. Opps. The page/node I was looking for came up as content in most of the other sites. Duplicate content. Quite a bit as a matter of fact. Not good when it comes to search engines. I had forgotten to set up the 302 redirect in the htaccess file. The result was that when spiders crawled www.example1.com, they would see content for the example1 site. But, when crawling example1.com, minus the 'www,' they were redirected to content on the parent site. Hence, many sites were sharing the same nodes as far as the search engines could tell. The fix is in your root htaccess file. Look for the section # Various rewrite rules. It will explain what to do. You may also want to check out John Forsythe's post about How Duplicate Content Hurts Drupal Sites. That article covers a lot of ground.