there are several ways of archiving the tweets!
yours is a very simple one however i prefer Doug Bowman’s {@stop} method, just create a new WordPress site either a fresh WordPress install or a site in MU! theme is available at http://stopdesign.com/archive/2010/04/30/tweet-archive-theme-files.html. Andy Graulund (@graulund) built a new php mySQL compatible script and mine is up and working at http://scrawlt.com/tweetnest/ thanks for this simple method however you should update the post saying you can’t retrieve the older tweets if you have already passed 3200 API limit use tweetscan to archive the older tweets because reader would start arching only the current tweets so if you need your older tweets too use tweetscan it provide the archive in many formats include excel sheet and XML!

thanks again!