iPhone app to follow/navigate an imported .gpx Is there an iPhone app that allows one to follow an imported .gpx track, in a car navigation-like way?

The apps I found so far, like Trails, can only display the track on a map. What I am looking for is a "download-and-forget" experience for my bike trips. I want to import a track and just look at my iPhone to tell me in which direction is the next waypoint, or how can I get back on track if I get lost.
http://www.motionx.com/ is the closest I've seen. You can set it's map to show track up as you ride. It doesn't know where the roads are though, nor zoom in or out depending on your speed, nor show upcoming turns. 

NOTE As of 2019, this app is now end-of-lifed. It was great while it lasted.