mindgarden said^Yes, but for most of the places that I drive, the GPS shows the speed limit as "no data."
Also, it seems to me that the voice navigation system is getting worse over time. Although it did once find a neat shortcut direct to the top of a freeway ramp for me, it often tries to direct me into dead-end neighborhoods, or up peoples driveways that it seems to think are thoroughfares.
The speed limit is often a temporary reduction from the normal posted speed for construction or an accident, that may change in a few hours. Even GPS combined with live traffic updates, used for instance for traffic accidents & delays, often will still reflect a time lag.
Which is why the Ford optical system offers an instant on-board response to the current speed limit signage. Except, I see limitations, especially in terms of visibility during rain, fog, and darkness.
Also, as I said earlier, how does the system distinguish between speed limit signs and road number signs? Furthermore, what is its scan area? What happens when you're on the Interstate, and an exit ramp has a lower speed posted, right next to the highway you're on? A human knows the sign refers to the exit speed only, as you continue driving past at full highway - can this device make that distinction?