What are the issues in using published RSS content from other sites in your own? Do you have to get permission from the RSS originator, or is it implied in the publication of the content?

I mean, if I'm starting a site for car fanciers, can I include RSS content from other car sites without their permission? Assuming, of course, I kept the link to their site & content & didn't re-label it as my own. I'm just interested in aggregating published content from other related sites to make mine an interesting portal. I don't want to make the user find his/her own RSS feeds and integrate them, like on My Yahoo, because most people will never bother to do that.

Since it's a special interest site, I'd like to do the grunt work to find relevant feeds and just put a bunch of headlines in the right column that the user can click on to go to the relevant article. I'm just worried if the sites I take the feeds from would feel I'm "stealing" their content since in some sense we could be competing...

Obviously, I am not an expert on RSS -- I tried searching for info on this, but couldn't find it.

Thanks for any insight,

Paul