I respectfully disagree. As someone who deals a lot with spam and abuse issues, there's basically nothing left to identify unique clients on the web. IP addres

I respectfully disagree. As someone who deals a lot with spam and abuse issues, there's basically nothing left to identify unique clients on the web. IP addresses definitely don't work and CAPTCHAs don't work either (they're broken by hordes of humans in low-income countries solving them in near-realtime). How would you prevent automated abuse? It's become a very difficult problem.