How accurate is the inflight location information?
The route is actually quite accurate; it is derived from the navigation system of the aircraft. You can determine your departure and arrival routes pretty well from the inflight entertainment system if you are familiar with the routes on the airport you are flying. 

In the image in your question you can see a slight course change East of Newfoundland. This is where the aircraft entered its oceanic track. 

If the system was operating on MH370, it would have shown the course change as well. 

Below you see what the IFE showed on 11 september 2001 when aircraft heading towards the USA were not allowed into US airspace after the attacks. 


Source: airliners.net