Originally posted by DavidPhillips
One thing that you could do is leave the user in the system and disable login for that user by setting the /etc/passwd entry for that person's login shell to something like /bin/false.
That would preserve the users files, name, and user id. Otherwise just remove the user and their files are removed as well.
While this is a good idea there are a few circumstances that might make it unfeasable. If you have a user that is causing problems they may have stuff sitting around still causing problems even if they can't log in.
After killing all their processes, it is wise to make sure they have no "cron" or "at" jobs. Then disable mail to their account. If you disable an account because they are running SETI or something on a machine and you don't allow that -- then you don't want their crontab to refire it up whenever you kill it.
It might be easier to just archive all their files with tar (you can even leave them on the disk if you want) and then delete the user. If the person needs their files you can give them the tarball. If you decide to let them back in, create the user and unpack the tarball again.