The Microsoft/Yahoo PPC alliance was always going to have teething troubles and give advertisers some headaches. We are gradually learning just where those are going to come from.

The most complicated issues are likely to spring from the differences in the way that Yahoo Search Marketing and Microsoft’s adCenter treat keywords. adCenter in general provides much finer control over management of keyword mis-spellings and plurals, significantly greater limits on negative keywords, as well as taking a different approach to geo-targeting.

Joseph Kerschbaum has written a nice summary of the important details. His recommendation for Yahoo PPC customers? Start setting up an adCenter account now, so that you don’t get caught out by the differences in approach.