Re: On the plus side
The distro-upgrade usually only works if you have a fairly simple mount arrangement, I have tried it and sometimes it works a charm, other time it failed miserably on machines with odd mounting setups and/or MD RAID in use.
My advice is always put /home on a separate partition, and if you have the space leave a blank ~50GB one as well. Next distro comes along, install it in the unused partition, and once working edit its /etc/fstab file to mount your old /home partition again.
Once happy, you can overwrite your old root partition when yet another new distro is available.