Slightly offtopic, but what are the legal implications of crawling a public website and building a derived service like this? I know it's usually considered gray area, but are there any clear limits? What does it take to build a legally stable business around scraping public content?

Citation from the Patreon Terms of Use on the public area: " Without limitation, you may not:

13. Use a robot, spider, manual and/or automatic processes or devices to data-mine, data-crawl, scrape or index the Service in any manner. "