Long time ago I worked with a few developers on some relatively simple web project. We were using php and smarty and we used svn for versioning. At one point some dude joined the project as a php developer (with a few years of experience).

After a few days without any commits, we found out that he doesn't know what a SVN is or how to use it. After he learned how to use it we found out in our repo bunch of files with a following naming scheme:

filename.php
filename_1.php
filename_2.php
filename_3.php
filename_4.php
filename_5.php