Is there a way to mark points of interest, and retain them on the map?  Say I found something interesting with my P-4 and I wish to go back to the same spot at a later date can I put that spot on my map?

For same flight path run and save waypoints, then use saved files again at later date ? Or if you look at the flight record the GPS co-ordinates of where the aircraft is during flight are displayed during playback.

I usually setup a POI on my cars satnav for future reference to take me back to same site.

You could create your own Googlemap with markers for all your POI.

Thanks Aardvark.........

You can play back your flight in the viewer and pause it at the spot where you want.  The GPS coordinates are shown in the viewer's control window where you paused it.