One of the most annoying problems with any social media platform is a low-level, continual spam barrage from companies that create sock puppet accounts to post their crap to forums, blogs, and discussion groups on sites like LinkedIn.
What amazes me is that so few sites are willing to take the Metafilter approach and just charge new members $5 to sign up.
Spamming sites is effective because it's low or no-cost for sending emails or creating accounts and then spamming users. When an account is whacked for spam, it's a very minor inconvenience for the spammer to create a new account.
If spammers had to pay $5 to create each account – and it was rapidly whacked for spamming – then the cost of spam would quickly outweigh the benefits.
Oh, and there's the minor benefit of actually putting money into the service.
The downside, of course, is that it would limit growth due to the fact that fewer users would be willing to lay out a credit card. However, that's not a bad thing. First, I'd rather have an audience that's engaged enough to pay the $5. The number of users who would be valuable to a service – but unwilling to pay anything to join – is pretty small. Second, you could easily integrate with Amazon payments and other services that take the pain out of account sign ups.
And if you're running a site that (oddly) doesn't need or want the money, give it to charity.
I keep hoping this model will catch on. I'd happily pay $5 for each site that I use heavily, if the trade-off is better comment quality and no/less spam.