I have got a couple of clients who rank fairly well on the UK Yahoo! for some pretty decent phrases who up until now have only been getting a couple of hundred uniques a week from it. It will be interesting to see if this improves things. I know for a fact that Yahoo.com can send some good traffic, it is just the UK version that up until now has never really sent any.
I do not know if this is working in other countries or not yet, it could just be UK IP addresses that are getting redirected.
Update: Flyerguy over at Webmaster World has confirmed that German IP addresses that visit Yahoo.com are now being redirected to http://de.yahoo.com. It looks like the changes could have been made worldwide.