I'm seeing nearly identical SERPs on Yahoo Japan and Google Japan now as well. I thought Yahoo Japan was going to alter the SERPs somewhat to make them unique. Right now it looks like Google took over the entire Japanese search market.
I agree with Garya. The old Yahoo Japan SERPs were better.
Looks like it's not occuring on all computers yet. My computer at home had the Google results, my computer at work has the old Yahoo results. My coworker who has the same IP & computer config as me has the Google results.
The number one easy difference between Yahoo results & Google is this: Search for any keyword & attach the .com or .jp at the end. If the result comes up at any position other than #1 it's a Google result. If there is a page that resolves on Yahoo it is always #1 position.
I read that some expect Yahoo Japan is going to have "Powered by Google" on it. I might be wrong on this one but I doubt that is going to happen.
System: The following message was spliced on to this thread from: http://www.webmasterworld.com/asia_pacific_search_engines/4233022.htm [webmasterworld.com] by bill - 3:49 pm on Nov 22, 2010 (jst +9) Today I noticed that Yahoo Japan has started showing the same organic results as Google Japan. Integrated into the search results are results from Yahoo Answers, Yahoo video, & Yahoo shopping.