Ask HN: How do you implement “Free Trial” logic in your application/SaaS?

I've never had to deal with such a scenario, but out of curiousity, how do you manage free trial users in your (web)app ? Is it just a boolean column in the DB ? Do you actually delete their info when their trial expires ? (What if they decide to sign up a couple of weeks later and want to access their data ?) Any gotchas maybe ? Thanks for sharing.