Chown has a nice feature that will allow you to change ownership of files and directories recursively for a single user without even needing to find them. First cd into the root source directory required to change ownership of the files/directories. Then use the chown –from= version of the command a la:
chown --from=<old_user>:<old_group> <new_user>:<new_group> * -R
Also works without groups, using the numeric uid instead of name etc.
I love the simple ones.