There used to be things called planets that aggregate all RSS feeds on a given subject. How legit are these sites? Can they legally repost the RSS contents (as much or as little it is supplied by the feed publisher and given the due credits)?
I believe Google News did just that and got in trouble with some news outlets. Is the legal landscape on these things a little clearer now?
You have to look at this on a per-feed basis. Some sites publish their content with open Creative Commons licensing, in which case it's perfectly fine to go ahead and republish them wholesale.
Overall, though, it's generally going to be okay to publish short excerpts of full-content feeds, or whatever is in the excerpt field(since that's the point of it). The expectation is that some reasonable credit is given and a link back to the original.
If you have real legal concerns about this beyond just curiosity, you need to talk to a lawyer.
