I started to do a little SEO (mainly external link building) for a friends Ebay store and while I really can't get much traction in the Google SERPs (except for a few small words), I seem to have climed to the top in Yahoo for many of the main key phrases.

This is weired since most of my SEO work usualy has the opposite effect, good results in Google and nothing to write home about from Yahoo!

Anyone have any idea why this might be?

The only thing I can think of is that Yahoo seems to have a relationship with Ebay.

Helps to "own" pages on an authority site.

Have you set-up and "About Me" page and given a link back to your websites? You are allowed to link out from that page and my links from there show in Yahoo! backlinks.

Well you get good SEO tutorials from google to build good optimization.

And better deal with yahoo by creating a yahoo sitemap