I had to bite the bullet and update my iPod Touch 4th gen from iOS 4.1 to 5.1 today. What a horrible experience! It took 3 hours of downloads and software updates to iTunes and the iPod. I was required to install half a dozen unidentified new apps and services on my computer that all need to communicate with Apple on the internet. I did all the recommended backups beforehand, but half-way through the update it reported an unexplained "error 5000 - all iPod contents will be lost if you proceed", and it did indeed lose all the music and most of the apps content of my iPod, and they are no longer backed up in iTunes. Fortunately I'm paranoid and backed up everything by alternative means since I don't trust iTunes one bit.
I compare this to the painless updates I've had with WebOS, and the ease of backing up and restoring content and apps on my TouchPad, and I don't know why anyone like Apple. Apple stinks!