Pfui - 1:13 pm on Sep 29, 2011 (gmt 0)

Speaking of Yahoo-specific UAs, this circa 2010 app's run by everyone other than Yahoo:

Yahoo! (iPhone Inquisitor; 1.0)

Thus far I've only seen it go for favicons, akin to its kin:

ycar8.mobile.bf1.yahoo.com
YahooCacheSystem

(Search for that UA on this site for info and threads.)