As part of our Feed Manager series, we've now released an x-cart product feed for Yahoo:
http://www.firetanksoftware.com/fts/customer/X-cart-Shopping-Feeds-cid-26.html
It works in the same fashion as all of our feeds giving you total flexibility. It comes as a stand alone add on (doesn't affect your x-cart at all) or as part of the all in one bundle Feed Manager pro.
Compatible with X-cart 3.4.X, x-cart 3.5.x, x-cart 4.0.x. And coming soom x-cart 4.1 compatiblity! (you can also pre-order this)