Fedora 18 "software": "check for update" hangs

[D. Hugh Redelmeier]

When I selected "Software" and within that chose the menu item to check 
for updates, the process worked for a while and then apparently made no 
more progress but ate 100% of the CPU.

It is kind of scary interrupting an update, but after about half an hour 
of no progress, I decided that there was no other way.

Do this in a superuser shell instead.  It works and gives better feedback:
    yum update

See https://bugzilla.redhat.com/show_bug.cgi?id=922697

PS. I consider software: check for updates less convenient than the 
pre-F18 "sofware updates".