Keep refreshing. You do NOT have to upgrade incrementally from 4.x.x to 4.x.y to 5.0. From what I got from Apple support (and right or wrong, it makes sense), not everyone was 'shown' the 5.0 update at the same time. The update wasn't posted on the Apple website until 12:00 PST (3:00 EST). Depending on your device, it wasn't "telling you" that there was an update until different times during the day in order to spread the download load out throughout the day.

My wife's iTunes was showing 5.0 at home before mine was at work. Her's was showing it available at about 10:45 and my computer didn't show it available until almost 2:30.

All of that fell apart once the direct download servers were known and published and people started hitting them directly and/or 12:00 PST hit and most everyone "saw" the update. The servers all but got crushed.