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.
Those minimum bids have now gone into affect, according to a WebmasterWorld thread. We knew it was coming this week, but we didn't know exactly when it would hit advertisers.
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.