Robert_Charlton - 5:38 am on Mar 23, 2001 (gmt 0)

It's clear to me on Google that the Yahoo category affects rankings. I don't know enough to generalize, but, say, in the area "widget store" or "widget stores," I've seen a listing in Regional> Widget Dealers> Location> Directories boost a search for the plural "location widget stores" much more than a listing in Regional> Widget Dealers> Location... which will boost you for "location widget store" singular, but not as much for the plural.

Not quite a precise example, but it should give you the idea.