I have Gentoo, CentOS, Mandriva, Debian, Ubuntu and Suse installed on one machine. I was wondering how others have managed user accounts in such an environment.

Since it is my own personal computer and I am its only user what I have done is to create a user directory in /home and then add a user in each distribution with the directory /home/username/<distribution>user

So when I log into gentoo as username my home directory is /home/username/gentoouser/
When I log into debian as username my home directory is /home/username/debianuser/
The skel for each distribution gets put into its own directory so I have .gnome .kde .bashrc in each of the distributionuser directories.

When I use mozilla I want to be able to use the same config directory so I setup a .mozilla directory in /home/username and then provide softlinks to this from each of the distribution specific directories.

I can do this for .xchat2 and .vimrc and a lot of other config directories that are not too distribution dependant.

I also have to be careful when constructing the user and group entries in /etc/passwd and /etc/group so that each user per distribution has the correct home directory and has corresponding User IDs and Group IDs.

How have others managed this situation and does anyone know of any user management tools for such an environment to make this process easier and less error prone.

Is having your home dir as a seperate partition and mounting it as /home/username in all of the os's an option?

You can have you home directory on a separate partition. You can partition you home directory across as many disks as you need. Schools can have separate partitions for teachers and students ie /home/teachers/teacher1 and /home/students/student1 with students and teachers on different physical disks. All unix type operating systems can do this.