Well, there's the real world answer, and the legal answer. Not too sure about the legal answer, thats always murky. Some things are copyrighted, some aren't. You can't just take someone's story, or art, and use it on your own site without permission. Usually the creator has all rights until they are given away. Even if they have uploaded it to another site, that doesn't mean they have given you permission though. On…
I guess my followup with that would be this: What if the user is submitting content that they would very clearly want re-distributed? I guess my question with that is, if you take the end-user who is submitting the content out of the equation, does the site that is being scraped from have any kind of leg to stand on if they don't want you scraping their content (excluding technical means that they might implement), a…
But like someone else said, if someone wants their content distributed, the user is not going to give you any trouble, and if they do, you're very protected if you take the offended material down right away, as someone else mentioned.
The website you're stealing from does have legal measures they can take, especially if you're directly competing with them. I think someone else mentioned that they could also just reconfigure their website to mess up your scrape, which is probably what they'll keep doing. They'll also likely publicize your bad business practices and you'll end up with a horrible reputation. Nobody likes a copier. Its like people who steal designs. They hardly ever outperform the website they're copying.