Yahoo told us to prepare for a minimum bid change, where now quality and value will impact an advertisers minimum bid for a keyword buy.
First reports suggest it happened sometime before midnight last night (EST). The first post was at 11:13pm (EST), and the next report was about thirty-minutes after midnight.
So far there has not been an out cry of advertisers being hit with minimum bids of $10, like with Google. I will keep an eye out for you and report back if things change.
Forum discussion at WebmasterWorld.
Update: Correction: Yahoo's Minimum Bid Interface Live, Not The New Pricing, see this new post for more details. Sorry about the confusion, we will keep watching and keep you up to date.