Yahoo has been shaking things up a bit for a while now.
LOL! What an understatement! Ever since they bought Overture, their programming has been all over the place in almost every area (spiders, reporting, etc.etc.) They seem to be having difficulties integrating with (or expunging) the Overture engineering team.
The bottom line is:
Good SEO practices are good for ALL spiders and ALL visitors.
There are some "tricks" and such that can temporarily influence some programs, like the "Google likes backlinks" comments illustrate, however these are not to be taken as the final word on what to do.
The best SERPS come from quality content married to clean code and appropriate SEO. Don't worry too much about the "trick of the day". If you keep it clean and useful, your SERPS will reflect that, and so will the directories.
Quality content begets backlinks, too, which add authority and improve your ranking in SEs that pay attention to that stuff.
If you are not showing up in Yahoo as you expect, take a hard look at (a) your code (use the W3C's validator
to get it perfect), (b) your content (is it really valuable or am I trying too hard to sell something?), and (c) your keyword density (maybe check out the tool for this at KeywordCount.com
to see how you compare to the competition).
Here's a brutal article about SEO for the big SEs, including Yahoo.
It's not too recent, but it includes some useful information that may help you.