Thanks for the question Alex. A lot of people don't really like my answers to this question. I think I may do a full post on the topic, but I'll give you the short version here.

First, lets just agree that the effort to go after people who re purpose our feeds and "steal" our content is generally not going to meet with a lot of success. There is too much of it, and the barriers consume a lot of time.

1. Use full internal links in your posts. Link to other content either on your site, or on other sites that lead back to your site. Make usre to use absolute links with the full http://yoursite domain.come/pathto/your content, not just pathto/yourcontent. This ensures that scraped and re purposed content leads back to you.

2. Publish only what you are Okay with having syndicated to your feeds. Most blogging software either has, or has plugins that have fairly sophisticated feed publishing options. You should be able to create feeds that give readers enough meat, while also encouraging the real fans to come back to the blog to read the whole scoop. This way, anyone who uses your feed is really just publishing an ad for your blog.

3. If you really really don't want people to syndicate any amount of your content, look into using an authenticated feed where your readers have to send their login to the xml to get the feed back. This will limit your subscriber base somewhat, but if your content is solid, the people who really want it will authenticate for it.