The problem with this question is, when you think about it, one big reason all the popular free web services ARE popular is because they're free. So pretty much my answer to any of the sites I use would be, I might be willing to pay if I couldn't find an alternative, yet at the same time, I'd probably never be using any of them in the first place if they weren't originally free. However, I would NEVER pay for social news/discussion sites like this one (or digg, reddit, etc.). Regardless of the quality of the stories and discussion, social news sites are services I only use in my leisure time, I would probably not visit them if I didn't have tons of spare time anyway. No offense to social news sites, it's just that I wouldn't pay for them.
That's a great answer. The question was an attempt to see what's entertaining but not valuable, and what's so unique that there's no good substitute for. For instance, there are other web based email clients (not as good as gmail) but there's no other community I've found as great as HN. Since I'm sort of technologically isolated, the community here is a godsend that's the most stimulating entertainment I get outside of my wife and kids.
