They don't have tool that shows who, what or even the price other advertisers are bidding. They have a tool for advertisers that gives traffic estimations based on your bid, but it is not accurate at all because your position depends on your CTR. A lower bid can get a higher placement if the ad has a higer CTR. It is very different than overture. Google does not break out content network bids, so there is no way to tell what advertisers are bidding for ads that run on publishers sites.
Probably because overture was doing it before they had a publisher program so there wasn't any harm in showing bids. While YPN publishers can now know what advertisers are bidding, they too, don't show who is participating the the content match program (what runs on YPN sites). You could see that a keyword "blue widgets" has 4 advertisers bidding around $5, and then the number 5 is bidding 50 cents and it goes down from there. You could build a website around "blue widgets" and then find out that those $5 advertisers don't participate in YPN, so the highest bid, as far as a publisher is concerned, would start at 50 cents. Yahoo also has far fewer advertisers than google, and there are a lot of wild swings in pricing - sometimes with just one advertiser dropping out of content match. I have one site where a single large advertiser affects the pricing by 400%. If they are running content match, clicks on the site pay 4X what they do than when they are not participating.