I've had mixed results when using the GUI updater.
What has never failed me is this method:
1) triple check your sources.list
2) run (as root), apt-get update
3) run (as root), apt-get upgrade -d
4) run (as root), apt-get upgrade
5) [if any errors in #4], run (as root), apt-get upgrade -f
6) run (as root), apt-get dist-upgrade -d
7) run (as root), apt-get dist-upgrade
8) [if any errors in #4], run (as root), apt-get dist-upgrade -f
9) reboot and test!
Always resulted in successful upgrades. I've been down the "destroyed" system route when upgrading before.
But like always, I do a quick clonezilla of my /root partition. I consider that critical. Even if the upgrade goes smooth, you never know what show-stoppers you'll run into after the upgrade (such as a particular critical application you use is not compatible with some of the updates). You always want a rollback strategy.
