I did a prototype for that idea back in the J2ME days when the first phones came out that had accelerometers. It works surprisingly well, provided you have lots of data (multiple cars driving through the same route to average out any random fluctuations due to driving style etc).
There were two issues:
1) It was way too early for this idea as the devices that had the HW for it were rather rare
2) I had no killer app that would entice people to install and run the app. There were no app-taxi companies at the time and just telling people that "please download and open that app when you are driving to help the local municipality fix the roads" wasn't really going to fly
I'd still love to work on that idea though.. one day :)
There were two issues: 1) It was way too early for this idea as the devices that had the HW for it were rather rare 2) I had no killer app that would entice people to install and run the app. There were no app-taxi companies at the time and just telling people that "please download and open that app when you are driving to help the local municipality fix the roads" wasn't really going to fly
I'd still love to work on that idea though.. one day :)