An example of a URL with session ID's:
http://www.webmaster-forum.net/forumdisplay.php?f=19
A cleaner URL:
http://www.webmaster-forum.net/forumdisplay.php?f=7
Nice summary John.
Would it not be better to rewrite the PHP based URLs to HTML using mod-rewrite?
I also feel that one should validate their pages regularly for W3C/XHTML compliance to make sure that the sites get indexed properly in the search engines.