The Via Amos 3000: A monitor-mountable Pico ITX board running at 500Mhz, with 1GB of RAM, gigabit ethernet, four USB, and DVI video, in a cool metal case with no fan. It can probably grill burgers too. [BBG]
Half the size of a Mac mini and half as useful is my guess.
For items like registers, kiosks, and the like you wouldn't want the case. If you needed something hazard proof (for inside a paint booth or chemical treatment) I doubt this thing would even qualify.
While the size is great, I really don't see it doing too well.