If your website is a target of web scrapers (http://en.wikipedia.org/wiki/Screen_scraping), here’s a simple way to keep them on their toes..
Every few days (or weeks) make a small change to the web page format. The trick is to make the change in such a way so that your users do not notice it or are not annoyed by the change. Most of the simple scrapers use, screen scraping and this would confuse the hell out of them 🙂 and usually deters the most abusive ones. The smart ones would have approached you in the first place, requesting permission to scrape or get authorized for an interface.
To take this a step further – the real trick is to find the “meat” of your page (i.e. what the scrappers are scraping for). Most scrapping is not particularly robust or error protected code – the most common approach is simply to grab an entire page as a string, and then hunting for some marker to begin parsing from (this site itself is a good example – a scrapping targeting this site would hunt for the div class=”entry” tag that begins the start of each article.
Once you know where the meat lies, it’s not that difficult a process to write a simple pre-processor that can munge your div tags and css tags on each deployment (or, say, once a week) to random nonsense names. Every time the CSS/div rotates, it will break the majority of scrappers out there.