By doing a search on google you can check if there are any unused gmail invites floating around the magic inter-web. All you need to search is "Thank you for testing site:http://mail.google.com/mail/" or use the url http://www.google.com/search?q=Thank+you+for+testing+site:http://mail.google.com/mail/&hl=en&lr= That will bring up all gmail invites that have not been used, and are in googles index, by putting in some unique text from the invite page, and narrowing it down to the pages in googles invite directory. Just thought I would throw that little find out there! BUT There were only two invites left when I searched it but you never know when new ones will pop up!
gone are the days we could sell our invites *sigh* but yeh, got loads of gmail invites if anyone wants one