Have have no problems in our development site keeping up with RC updates via Dashboard. Was anxious to kick it to 3.0 final today and let it rest a while while we finish the site, but bad news which clearly others or having problems too.
Just wanted to add this as it is indicated or assumed that many of these update fails are 2.92 or older to 3.0 - in our case, it died from 3.0RC2 to 3.0 final.
Update is taking much longer than the 3.0RC versions did - thought it might be download/traffic issues but I'm watching FTP and download files are there pretty quickly.
I'm going back to RC2 and sit awhile I guess.