I've got a script on a few of my sites. Initially, the redirect is off. If it passes 100 incoming hits from HN in an hour, I assume it's on the front page. Then I just do some messy scripting to re-enable the script for a few minutes every hour. One minute on, seven minutes off. That sort of thing. Basically, the goal is to redirect the maximum number of people, and you can't do that if it redirects everyone. No, I won't be sharing these scripts with anyone but mostly because they're all terrible kludges that do not deserve to see the light of day.