It appears that some folks are buzzing about a new update taking place at Yahoo Search.
A DigitalPoint Forums thread has one person documenting a major change in traffic from Yahoo:
Just like every morning I am checking my SERP's through the Keyword Ranking tool here at DP and to my astonishment I found that 90% of my sites lost rankings in Yahoo...
Most rankings have declined from top3 into lower top 10 or even top50 and my previous top10 rankings are now nearing the 100. ALL my hotel related sites lost rankings, while some of my other sites have gained some, but that is from outside top200 into top100.
This leads me to believe that they did on algo update today, but I would like to have some input from you all.
I personally reviewed a couple of my sites and noticed a decline in traffic from Yahoo on some sites and an increase in traffic from Yahoo on other sites. It may just be too early to tell. The last update was just about a month ago, so it does make sense that this can be an update.
Forum discussion at DigitalPoint Forums.
Update: Now there is chatter about an update at WebmasterWorld.
Update 2: Yahoo Search Blog has confirmed the update saying:
Over the last few days, we've been rolling out some changes to our crawling, indexing and ranking algorithms. While we expect the update will be completed soon, as you know, throughout this process you may see some ranking changes and page shuffling in the index.