Just used PE on a trip down to Costa Rica and it worked quite well. I really like this app, being a map junkie.
Anyways, a couple of times I missed a turn or two because we weren’t actively paying attention to the route on the screen — it would be extremely helpful if the phone will trigger some audible cue (a ding, or some kind of sound) when you are at a point that you were supposed to turn to. If the phone is on “silence” mode then it could trigger a vibration instead. If the phone is in the background, pushing a local notification would be extremely helpful as well.
Also, another helpful cue would be to possibly change the color of the transparent ribbon indicating your next turn, so that it changes colors as you are approaching the point — ie blue when you are a mile away, yellow when you are half a mile, green when you are at the turn point (plus audible cue) and red when you passed it and you are now off route). The distance/warning ratio would depend on the speed.
Thanks and keep up the good work!