1. This would surely hamper growth for real users. No one wants to verify email or catchpa. 2. Tinyurl could help them, but also there's a million affiliate pr

1. This would surely hamper growth for real users. No one wants to verify email or catchpa. 2. Tinyurl could help them, but also there's a million affiliate programs out there, you could paste a different affiliate link each time. Also surely a lot of accounts legitimately contain links from the same domain - eg new blog posts. 3. This example was using hashtags, but also just popular search terms - "american idol". I don't see how you can detect that easily. 4,5. Agreed, those I think could work well