When genuine users subscribe to RSS feed to keep updated with new content to read is understandable (and so for search engines). But in my experience it appears that publishing RSS feed is like giving away original content on platter to site scrapers. The people extract RSS feeds and publish on their site (with all sorts nofollow techniques) Any opinions, suggestions to bust these people??
For every scraper that uses nofollow there are 5 that use proper links. Linking to good resources improves your rankings so there is no reason to use nofollow. Also as long as you keep the RSS description to a minimum you are hardly giving away your content.