This is crazy... but my iPad backup was running for over 20hrs and NEVER completed successfully. This meant I was not able to upgrade to 4.2 because iTunes FORCES a backup before the upgrade.
Yesterday I was completely frustrated. I did all the things people are talking about on this forum to solve it: Deleted magazine apps, deleted GooodReader and all files, used the original iPad cable, uninstalled and reinstalled iTunes, did a hard reboot of my iPad, etc, etc. NOTHING CHANGED ANYTHING. Still was running for 20hrs and finally just stopped. (Of course this took up lots of my time over the last week trying new things and letting the backup run unsuccessfully -- and very frustrating.)
But yesterday a friend on Twitter suggested using an app called BackOff. It's online here and is free: www (dot) digidna (dot) net /products /backoff
It WORKED! At least it turned off the automatic backup on iTunes. So when I ran the upgrade, it skipped the forced backup and went right to the upgrade and WORKED fine.
So now at least I have 4.2 on my iPad. Now I'm going to try running a separate backup of my iPad and see if the new iOS helps with backups speed... Who knows?
Anyway... it's not a perfect solution because I still don't have a backup, but at least I now have iPad folders, multitasking, printing, and all the nifty goodies on 4.2... :-)