I was thinking for a while that it's a matter of time until there is some serious accident where a Tesla driver is using the screen for something distractive while driving, and being heads down gets sucked into that 17 inch "TV" - then hitting a pedestrian for instance. Heads Up display would solve that, and would be even better than the centre 17" screen, though that's for a future model, not for the model S in its current version.
I know of other cars where any screens within the drivers view, that can show video or other entertainment, are blanked while in motion, while the typical screens in the back of the headrest (for the back seats), are unaffected.
I hope Tesla will come up with something like this as a solution.
If there was some option where only the front passenger could use the web screen while in motion, that would be great, but I'm not sure how that could be implemented. A privacy screen that prevents view from the right side (for the RHD model), activated automatically when vehicle is in motion AND the web function is enabled?
Too complicated, really, as it was mentioned - most people have mobile devices anyway, so a motion vs parked function would be sufficient I believe.