I've killed off the feeds on a few on my WP powered sites, and it seems like the rankings/traffic are going up. I got sick of scraper sites out ranking me for MY OWN CONTENT, so I pulled my RSS feeds down. It seems to be working for me. Anyone else done the same?
I think more effective could by adding random copyright message in your feed. This would also get you some extra backlinks. But you are right, scraper sites are one of the biggest problem of web 2.0
Use their scrapping to your advantage and put a link on your articles. Thus, you will have more backlinks