It happens when no one is paying attention to it.
Most people get someone to come in and clean up the mess.
Figure i take care of this lan, 10 subnets and over 80 switches. 150 windows servers and 150 Novell servers, our wireless lan, a 30 server citrix farm plus backups for all of these (just at my site alone), global LAN duties and global server duties.
I allowed the desktop team into my closets to plugin cables as they needed and the "before" pics are what i got for my idea of making it easier on them and me...safe to say it wont be happening anymore.
I do use different color lines now (red for printers - Yellow for RoadRunner connections for visitors, green for wireless access points.)