Apparently disabling UAC had a weird side-effect: Onfolio doesn't work anymore! Onfolio is a Windows Live Toolbar add-on that displays RSS feeds in a "newspaper" format inside of Internet Explorer. If you turn off UAC, Onfolio's newspapers no longer work, and show script errors. Arg... why!?

So I guess UAC will have to be on for now, and I'll just deal with the iTunes problems for now, and hope Apple fixes it soon.