Sounds neat, but...
Recently a nearby road (dual carriage way between airport and business park) changed from a mix of 40,45 and 35mph speeds to 45mph unilaterally. If the adaptive cruise control hit this area it may make unpredictable slow downs where the old slower limits were. How in sync would Navteq be with all the cities and counties nationwide?
Recently, driving the improved Hwy 84 from Fremont to Livermore my Navteq enabled Verizon Wireless phone was insisting I was "not on a road, please return to highway". I could see my position relative to the old serpentine road on the map, and I could see the old road being removed by big yellow machines. Again, the road had been open a couple of weeks, and the database not propagated.
Even if Navteq (or other service provider) received adequate warnings of change would they be able to cope with delayed or early openings, temporary closures or redirects etc.
A driving aid, at the end of the day, is not a replacement for a driver, it is to assist. But we all know how we rely on assistance once we have it.
Overall, yes I would like that technology deployed.