"A BIG BALL OF MUD is haphazardly structured, sprawling, sloppy, duct-tape and bailing wire, spaghetti code jungle. We’ve all seen them. These systems show unmistakable signs of unregulated growth, and repeated, expedient repair."I'm sure everyone has seen one, worked on one, and even created one. I'm also certain that in general things aren't much different since that paper was first published in 1999. Here is a link to a "Big Ball Of Mud" Google video presentation by Brian Foote from August 2007. I guess that since the authors are still talking about the pattern we should expect it to be around for a while longer.
The next time you need to wade into the swamp, you might want to take a copy of the book "Working Effectively with Legacy Code" with you.