Much more precise information about the number of backlinks cached by Google is available at http://www.google.com/webmasters/tools/. A nice blog article about is at http://searchengineland.com/070205-165836.php .
Here is Matt Cutt's announcement: http://www.mattcutts.com/blog/google-provides-backlink-tool-for-site-owners/
It was also announced on the Official Google Webmaster Central Blog: Finally there is a definitive answer for all those newbs who ask "why doesn't Google show all my backlinks?".