I keep reading "crawl Facebook". How viable is that kind of thing? I could think of various ways to use the data (like I proposed a friend I could create a serv

I keep reading "crawl Facebook". How viable is that kind of thing? I could think of various ways to use the data (like I proposed a friend I could create a service that would help him identify the woman he did not approach - as a bonus, that project might boost privacy awareness). But I assumed that crawling Facebook would not be appreciated by Facebook, and also easily prevented by Facebook. Since there are 500 million profiles to crawl, a lot of different IP addresses for the crawler would be required. Also, how legal is it to actually use data from such scrapes?