Wanting to keep pages out of the SERPS that I felt shouldn’t be there I started using the following robots.txt file on a SimpleMachines forum site of mine.
User-Agent: * Disallow: /index.php?action=search Disallow: /index.php?action=calendar Disallow: /index.php?action=login Disallow: /index.php?action=register Disallow: /index.php?action=profile Disallow: /index.php?action=stats Disallow: /index.php?action=activate Disallow: /index.php?action=help Disallow: /index.php?action=admin Disallow: /index.php?action=pm Disallow: /index.php?action=mlist Disallow: /index.php?action=notify Disallow: /index.php?action=post Disallow: /index.php?action=markasread Disallow: /index.php?action=sendtopic Disallow: /index.php?action=printpage Disallow: /attachments/ Disallow: /avatars/ Disallow: /Packages/ Disallow: /sitemaps/ Disallow: /Smileys/ Disallow: /Sources/ Disallow: /Themes/