There's the satisfaction of placing the final piece, but what other motivation is there really for completing a 2D puzzle? Not much. That's why these 3D puzzles from Eureka are a better use of your leisure time since you're left with a surprisingly detailed model car in the end.
Available in versions featuring cars like the Lamborghini Murciélago, the Hummer H2, and even the Mini Cooper, like with a regular 2D puzzle you're not guided step-by-step through the assembly process. Think of it lik building an old Lego set you lost the instructions for years ago.
But so that assembly isn't completely impossible, every layer has a special piece with a raised section letting you know when it's time to move on to the next layer up, and so forth. Working from the bottom to the top, eventually you'll have a completed car if you don't run out of patience first. And for about $US30 you end up with something you can display on a shelf without needing to shellac it in glue first. [Eureka via Wink Fun]