The guitar player skeleton appeared in 2005. In 2006 I made another skeleton, placed it in a plywood coffin, propped on my lawn: less engineering, but also less action.
I believe the next skeleton will be climbing out of the coffin...
UPDATE 2007: My belief turned out to be unfounded: the next skeleton was, in fact, using a laptop computer.
UPDATE 2008: No Skeleton. Gourdzilla, the Dino-Pumpkin instead.
UPDATE 2009: The Skeleton is back. This year he's reading "Upgrading and Repairing PCs" by Scott Mueller.
UPDATE 2010: Skeleton pumpkin carving a pumpkin. Only tangentially gross.
Used in combination with all of the other sinister ideas out there (light-up eyes, motion-sensor scary voices...), the possibilities are endless.
I live in Humboldt County, Ca., a very soggy location where everything composts in minutes, but even in this anti-pumpkin environment, the skeleton looked great for almost a week.
Of course, the decay looked fantastic, too... The entire assembly becomes a liquid mess at a certain point. It's up to you to decide just when to peel it apart and toss it in the compost bin.
On a side note, one free-hanging skull I made dried out like a shrunken head, and lasted long past Easter. Could the whole skeleton be dried out like that too? Perhaps someone (who lives in a drier location) should try that...