This is probably an edge case, but we had a tftp directory that we were cleaning up based on last modified time. The problem we ran into is that Windows/Samba and Konqueror all maintained the original timestamps on the file. So when someone copied a file created back in 2006 over to the system it got deleted fairly quickly!

Our workaround was to make sure the files were not being backed up and then use the last access time instead of the last modified time.