You can keep, (and reuse,
without reformatting) your home
partition but you should
not reuse your home
directory between distros.
The reason for this is all those
.files that hold distro-specific and release-specific configuration information. They'll cause havoc / things will be lost if you start writing to your old home directory from a new distro. Trust me on this one, I have tried it in the past.
My advice is to make a new username for your new distro. By all means, put it on your original
/home partition if there's room: Eg if Debian UN =
anthony make (k)ubuntu UN =
tony. That way tony gets the default configuration files set up right for ubuntu, and you can then work out how to copy your data (as opposed to configuration) files from anthony -> tony. You'll have to set up all your configuration preferences from scratch for the new username & new distro. Yes, it's a pain, but you get used to it. No worse than win3.11 -> win98 (at which point I quit win altogether!)
Simple data files (music, documents etc) are easy to copy over. EMails have always given me headaches, but so far, it has always been possible, albeit with a bit of head-scratching and one secure
read-only backup of my original home directory that doesn't get deleted until I have a been happily running the new system for a couple of weeks.
/usr /var and
/tmp should all be reformatted: there is nothing worth keeping there.
