It has been observed that Yahoo! has removed the block result feature from My Web. Well, the FAQ has not been updated yet. The FAQ still says that the feature is available. It goes like this:
Can I block a site from ever showing in my search results?
Yes. Use the Block link in any search result to block that site from showing in search results for all subsequent searches.
To review and edit your list of blocked sites, click the Show blocked link under the results set or the Blocked link under Go To in the My Web management Pages or Tags tabs.
Even if you visit Yahoo! and search with My Web on any term, you would find only "More from this site" and "save" features. The "Block" link has been removed.
Now, it would be interesting to see if it comes under the tag spam issues. Yahoo! can’t deny the possibility of something like this in future.