The summary says it all. I can't possibly see why it's there, unless the author *meant* to put IUSE="", and then someone repomanned the ebuild later; inserted the IUSE="" at the top, and didn't see the USE="". I think it should be removed. :)
yeah... *someone* probably missed the I next to the U ;)... I uh... wonder who... uh... that could've been... hmm...
let's just sweep this little embarassment under the rug now ;)... all fixed in portage.