It seems like some webmasters are becoming fed up with the activity of Yahoo's crawl, Yahoo Slurp, relative to the amount of traffic Yahoo Search is sending the web site. In fact, some webmasters have taken the plunge and banned Yahoo from crawling their sites.
It is funny, because some webmasters were or are afraid to ban Yahoo because they think it might have some sort of impact on their Google results. One such webmaster got over it and decided to ban Yahoo despite his fears.
There is a thread at WebmasterWorld discussing the pros and cons. Some also wonder that will banning Yahoo have a negative impact on the Yahoo SearchScan & McCafee partnership and might have your site marked as harmful? I doubt it.
If you want to block Yahoo Slurp, learn how to at this page.
Forum discussion at WebmasterWorld.