From the OpenID listserv it appears that Yahoo! would prefer RPs to put a Yahoo! logo on their site that is clickable to enable Yahoo! users (and others) to login to that site (using the "directed identity" flow).
Also, looking at the Blogger implementation of accepting OpenIDs they list 4 main OpenID providers (I'm guessing Yahoo! will be added to the list) and then a button for "Any OpenID".
Maybe lesser known, but propeller.com (an AOL property) which accepts OpenIDs uses the OpenID protocol to authenticate AOL/AIM users but presents the UI as "Sign in using my AOL Screen Name".
What I find fascinating about this trend is that it bypasses one of the benefits of an OpenID (built in IdP discovery). Basically, these main stream RP sites are using the "User picks their IdP" solution for determining where to send the user rather than having the user type in their IdP (yahoo.com, openid.aol.com, etc) or full OpenID URL. At the moment, this scales OK as there aren't that many mainstream providers, but either user education needs to get better so this mechanism isn't needed, or we need a different technical solution.