You can have more than one user name in the /home partition. You may use
separate ones for Mandriva and Suse for example. I typically use roy-u for
Ubuntu and roy-s for SUSE. Then I drag files and folders that I want to share to
the new user directory, either moving or copying them as I choose.
Once I am sure that I am going to stick with a distro, I delete the other user
accounts. Once you know is where your Firefox bookmarks and mail are stored it
is easy to just drag them around wherever you go. Documents may be stored in
their original folders and opened as needed from their previous location or
dragged to the new user account as you wish.

KDE settings are harder to find. Settings specific to KDE all reside inside the
.kde/share/apps/ folder instead of separately for each application. I keep my
fonts in the .fonts folder. I now have over 7000 fonts which is far too many,
but I am too lazy to go through them. It is on my "Someday" list which never
seems to get done.