Everyone seems to be linking to The Register's interview with a link spammer. This is what caught my attention:

"The hardest form to spam is that which requires manual authentication such as captchas. Or those where you have to reply to an email, click on a link in it; though that can be automated too. Those where you have to register and click on links, they're hard as well. And if you change the folder names where things usually reside, that's a challenge, because you just gather lists of installations' folder names." So now you see why I'm using TypeKey.