I found this out as well - I was thinking Wow, OVI maps actually does do turn-by-turn tracking, what are all these guys talking about when they say it doesn't???....until I took a wrong turn!

The OVI map software doesn't really seem to care if you don't follow the route it tells you to and it doesn't go about trying to compute an alternative route once you stray off. This is really too bad since it seems it wouldn't take much programming to just have it recompute a new route automatically once your actual GPS coordinates are a certain distance away from the planned route.
I don't consider voice directions very important but certainly telling you how to "get back on track" once you deviate from your planned route is critical. Maybe next version...

-=AC=-