how would you protect a URL redirection service from spam?
thorax: For ri.ms and tinyarro.ws, we've actually seen significant reduction in spam just by banning abusive IP addresses. So far, that has had the biggest bang for the buck in terms of dropping spam considerably.In other words, we periodically do human review and obvious spammers are IP banned. It's a neverending problem, but they don't use so many IPs that things are out of control.If you do come up with a better approach that doesn't ruin usability, I'd love to hear it, too!