Looking at the options now...
Originally Posted by Rodayo
The 'Upgrade Ubuntu XX.XX to XX.XX' option says it will keep programs where possible, so I don't know what that leaves you with when it is done relative to what you would end up with if you run update-manager from within your existing installation.
So unless you planned ahead and actually created a separate home partition, there is no quick and reliable way to preserve home and have it be like a clean install + /home on separate partition.
I have seen other people indicate they have re-installed without reformatting, in which case you run the risk of having stuff spread about that the installer doesn't know about if you choose to do it half-*** (don't delete anything) or manually delete everything not in your home directories after booting the live session and before installation which is time consuming, but an option none the less, maybe.
I believe when installing Debian formatting your '/' partition is always done, for the rest of your partitions it is optional, so if the underlying stuff that does the actual partitioning in Ubiquity is the same as the stuff that does the actual work for the Debian installer, I don't know if you can rely on the option to not format your '/' partition to always be there. It's not something I do, so not something I check for.
Personally if I decided I wanted to start using a separate home parition after the fact, I would shrink the existing partition by the amount I wanted my OS partition to be, create a new partition in the free space to be used for the OS, delete any files that exist outside of the old home directory. Mount the old partition again if necessarry. Open a terminal window and type something along the lines of
so when you mount the partition at '/home' things will be where they should '/home/*' instead of '/home/home/*'
mv * ../
If you prefer using cut and paste in the file manager, that's probably fine too.
There are other options depending on how many drives/partitions you have and how they are used.
Personally I prefer to keep stuff on other partitions, one for MythTV recordings, one for music, another for everything else for example, have each OS keep it's own home directory in it's own partition, using descriptive labels for the partitions so I have the option of using the label instead of the UUID when mounting. This way there is not much if anything in my home directory to save at any given time, bookmarks, email and some miscellaneous riff raff.
If you only have one user in each installation and use the same user name, shouldn't be any big thing, unless the distributions disagree about the numerical ID the first user should be given.
If you have multiple users in one installation or use different user names in different installations and want to share files between them, if you create a group with the same name and numerical ID in each Linux installation and chown/chmod the directories/files you want to allow access to
if you don't want people other than the owner or group allowed access to the files use 'o=' with no arguments following, I believe if you want people in the group to be able to read all the files, but only allow the person that creates a file to delete it you would use the 't' option '
chown -R :group /some/location/*
chmod -R g=rwxs,o=rX /some/location/*
I have to look this stuff up all the time, but between the man pages for chmod and http://www.dartmouth.edu/~rc/help/faq/permissions.html I believe my examples are correct, it's not exactly clear what happens when there are symbolic links, you may have to chmod the targets of the links separately.
chmod -R g=rwxst,o= /some/location/*