A search on google at Yahoo! Search confirms this to be true. In the past the results looked like:
Notice the category link, which links the search result directly to the category it belongs to within the Yahoo! Directory. Now that seems to be gone for all searches I tested.
Same with a search on search engine roundtable:
Old Result:
New Result:
I tried several different searches that I knew returned the category link within the listings, and all are gone. I do not know if this is on purpose, or if this is just a Yahoo! test.
Forum discussion at Search Engine Roundtable Forums.

Comments:
No Name
03/26/2007 11:01 pm
This is actually quite sad, previously you could find more sites of similarity by it's classification.
cher
04/07/2007 07:14 pm
Its our hard-earned money, and yahoo doesn't care about this. If this removal is true, then it should return our money.
juan
04/26/2007 08:00 pm
Bad for us!!! like a post that I see, yahoo doesn`t care about this.
Jack Roberts
05/08/2007 01:51 pm
David, this is a keen observation and great graphic display of the move away from directory listings. Directory listings often lead to stale search results and can be difficult to manage and keep fresh. The major search engines which prefer to deliver spidered results that are typically more content relevant. Directory listings themselves are still important for websites and can provide quality traffic and also some link popularity for companies.