Also, you can only use a light pen by poking at the screen with it. A mouse can be set up so you can move across the entire screen with a much smaller and less physically demanding wrist movement.
I used to have an A4 graphics tablet, and while it was good for drawing, it was a huge pain to use as a pointing device - I had to make huge swooping arcs with my forearm to move the pointer, and it soon became tiring.
Engelbart's idea of 'efficiency' was as much ahead of the time as the mouse was. He didn't just point and guess - he produced empirical models which measured accurately how easy it was to use each device.
The only thing which might be easier to use than a mouse is an eye tracker combined with a finger switch - there are commercial (military/med) products which work like this, but they're not as cheap as a $50 rodent.
I was hoping by now we could have something like a fine grain touch screen tablet A3 size: that would solve the feedback problem in that you'd be looking at what you drew. You can't be me, I'm taken
I had one of these for a while - one thing it isn't is light.
The other thing it isn't is accurate - the drawing accuracy drifted noticeably towards the edges.
There's a new generation of multitouch products due next year. A 22-24" multitouch interface light enough to keep on my lap is probably all I'd ever want for music, graphics and general browsing.
