And it's not even the speed limit, it's the recommended speed for that exit. IOW, go as fast as you like, right up to the posted speed limit, but if you're a tall semi hauling a load it is recommended that you slow to the speed posted on the yellow sign. But I digress...
> Finally: we do not have any plans to automatically add any of this detected information to OSM. Any improvements will always be made manually by mappers through the existing JOSM plugin, iD integration (coming) and MapRoulette.
This points the way forward for OSM. OSM is a human map made from user contributions - the collected set of users' enthusiasms. That's what differentiates it from other maps. But that shouldn't mean that mapping should be a laborious process. The more innovations like this that remove the gruntwork from mapping, the better. (Same applies to recognising geometries from imagery and sensor data, etc.)
A map is one of the oldest forms of written communication. Some people think maps came before written language and as such are an intrinsic part of what it means to be human. Just think of the amount of information being conveyed by a map! We don't accept computers making other written works, why accept computers making our maps?