I do RSS feeds in both directions. They are important enough that Google has a seperate crawler for feeds. I get a visit from it twice a day. My outgoing feeds contain partial content from the forum which we have on its own class C IP and the links back to the sites and generate traffic that is very targeted. Any time someone comes to my site off of the feed links they are very definitely interested in what is on the site. So doing the feeds is a big gain with very little work.
I also use incoming feeds that bring me traffic. Every day I am getting top 10 SERPs because of keywords in the feeds that are on my pages. The feeds I bring in are related to my content but not 100%. So some of the traffic they generate is of the "look and leave" variety, but some of it genrates "site explorers" who stay on the site and look at a lot of pages. The evidence I have seen so far is that there is no penalty for carrying the feeds, and if anything Google is rewarding me, by giving me credit for keywords that are in the feeds.
There are some very powerful traffic generators that don't cost anything. In April one of my members had their site hit the front page of Digg, and for three days they were buried in traffic, and because it got blogged by some of the Digg community he got a lasting effect out of it. On his front page he has a link to my site. It was generally worth 25-30 hits a week. When he got the hit from Digg I averaged 300 hits a day for the big three days and the numbers from his site have stayed at around 100 a week. Plus a lot of the visitors from that burst picked up my feeds for their own site and I get the hits from those, and the additional backlinks.
When a site makes a feed available, there are no copyright issues as long as you attribute the source and leave their link in the content. It is being made available specifically for presentation on other sites. I think the only way you would get into an issue is if you use the feed for primary content and sell ads based on the imported content.