In the x86_64 fc6 prerelease:
I can't get yum to install anything from extras and can't see why
it shouldn't be able to.
I poked and prodded a bunch of things and finally gave up
and submitted this bug:
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=208778
I see some other mail that sounds as if I'm not the only one
with update problems in the prerelease.
Maybe we'll have the fc6 penultimate release next :-).