Welcome to WebmasterWorld Guest from 126.96.36.199
Are there any considerable downsides of doing this? Is it a worthwhile practice?
Just a comment... You should also allow the rewrite to occur if the referrer is blank. Many people using Norton Internet Security, certain firewalls, corporate proxy servers, etc. will have their HTTP_REFERER field blocked (and may not have a choice about it), and might otherwise perceive your site to be broken.