[Fang_]

> Would this violate the terms of service of a system like Facebook?

Yep. As far as I'm aware they don't allow you to display Facebook content next to content of competing sites, like Twitter. But if everyone's doing that locally on their own machines, how will Facebook know? And what can they do to stop them?

If the API is being used, they can take that away. But website scraping will remain as a viable (if slightly sub-optimal) way of getting the data out. Facebook won't stop its users from using its website, after all.