Yahoo has just done a major update of it's search results, more info. here: http://www.seoco.co.uk/blog/2007/05/23/yahoo-update-230507/
I notice a great improvement across all my sites but it looks like we are back to the good ranking we were half a year ago. That shows again to be patient with yahoo. I look at it as a bonus to the hard SEO work I do for GOOGLE
Definitely a boost to SERPs if you have good backlinks. I noticed quite a jump on many keywords across dozens of sites.
Yahoo is updating its SERPs from last night and this update seems to be very postive for my websites. I have already seen boost in my rankings as well as traffic with lots of competitive keywords and hoping for more traffic in upcoming days For further detail check yahoo official news at ysearchblog.com/archives/000455.html