I just noticed this about a week ago. I suppose it isn't that difficult, but it's first time I saw Google doing it.
If you take a look at [url=http://216.239.39.104/search?sourceid=navclient&ie=UTF-8&oe=UTF-8&q=cache:http%3A%2F%2Fwww.plasmaconnection.com% 2F]Google's cache of PlasmaConnection.com you'll see session ID's in all the links. Up until recently this prevented Google from indexing all the pages.
Then Google suddenly indexed all the pages, and interior pages are showing backlinks from all other interior pages. Google indexed it, regardless of the session ID's. It apprently knew to drop everything after the "&".
