It appears from the forums that we have early reports of a big Yahoo! Search update underway.
WebmasterWorld moderator, Sugarrae posted a thread at WebmasterWorld saying;
I'm seeing very big changes in the index this evening... looks like a big update in backlinks and some very big shifting in the serps for the areas I track. Also, that whole title change thing looks like a plague spreading through the web at the moment.
No official confirmation yet from the Yahoo! Search Blog but we typically beat Yahoo! to posted about their own updates.
Confirmed: Yahoo! posted at the Yahoo! Search Blog a weather report confirming the update:
We are in the process of rolling out some changes to our search results. As usual, you may be seeing some changes in ranking as well as some shuffling of the pages that are included in the index throughout this process. This update began last night and should be complete very soon.
Keep the feedback coming!
Priyank Garg Yahoo! Search