Apple is now collecting anonymous traffic data to build a crowd-sourced traffic database with the goal of providing iPhone users an improved traffic service in the next couple of years.
Steve Jobs added more during his interview with Mobilized:
We mention the traffic service and I think that is all we are going to mention at this point in time before we have something to announce. [...] We are building a crowdsourced database based on traffic and that is what we are saying.
Apple is collecting location data for Wi-Fi routers an using that to build out their home-grown replacement for Skyhook. Was Apple referring to a network traffic database?
It's possible "traffic" could mean road traffic, which would imply improvements to the Maps app, possibly including turn-by-turn navigation. Apple built their own Maps app wrapper for Google maps way back in iOS 1 (iPhone OS 1) and while they've added Street View and a few other features over the years, they haven't really kept pace with Google's own maps app on Android, especially Google Maps Navigation. They have, however, rolled their own location database, and bought map companies PlaceBase and Poly9, and have been rumored to be updating iOS Maps for a while now.
Hopefully we won't have to wait too long to find out!
Update: Per comments below, it does make more sense as a network traffic optimization feature. Drat. There goes my turn by turn! [Thanks Ren!]