Thanks for looking into it. I have a new version being beta tested and one of the new options is the choice of selecting threads based on thread start or on last post. Also it will have uShop integration, posting of the result in a "Winners Post", replacement variables in the thread title, and some more small things.
About testing the lastrun, you can have multiple rules, 1 running every day, and one running on a weekly or monthly schedule. The cronjob will need to run every day in this scenario, and only execute those rules that are supposed to be executed. Don't get what you say about lastrun never being lower then $cut, but will check it against the code tomorrow.
PS If you are just starting up, you could also help beta testing the new version