This was something that had been coming, but it was unknown exactly when the date would be. Yahoo and Microsoft have made an alliance. It’s called the “Search Alliance”. Originally it was intended as a unification for paid advertisements, but it’s clear now that the unification is for both paid and organic listings; do a search on both Yahoo and Bing for a keyword phrase, and the results are now identical.
It’s clear from a bit of research that this change means that Yahoo’s search algorithm is no longer being used, and all Yahoo results now mimic Bing’s results.
This does greatly affect SEO, since the way Yahoo used to rank differed from how you could rank on Bing. Now all strategies are moving towards the Bing search engine algorithm for ranking on either engine.
Whether or not this is a test or a permanent change we’ll have to see, but it’s clear that both engines are now united, perhaps in an effort to make a dent into Google’s crown over the search market.