Good idea. Have you guys seen these robot blocks yet?
They look very cute. I want to out FEZ in a cubelet!
I was thinking along the same lines. If you did it right, you could have an on-ramp from simple toys/hobbiest all the way up to light industrial to make prototypes and even production. Naturally robots, sensor devices, cnc. Think of how many people are recreating the wheel each time they want to do a cnc device? Custom cut hardware, custom sw, custom that. Too many disiplins required.
I would use socket cap head screws instead of magnets to allow more serious work and motion, but still be super quick and easy and strong. The concepts scales and is composable. Composable hardware - my dream! Like Live-Gadetteer blocks. Real legos for bigger people. This falls in line with my 1" grid system idea for hardware and components. The blocks, rails, connectors and linkages would all pattern off a common grid so everything hooks up - no custom drilling. I have some good ideas for this spinning. I need a cad/cam person and a 3d printer.
I saw them this week. I love the idea, I love the look, I love how they work.
But they are rather expensive :o
I wanna see a netmf version of this 
I do well with random desk gadgets, gives me something to do when I need to work my way down the stack of a 5 layer application tracking down that elusive bug.
Problem with this is that it looks really too limited for the cost…