I UPGRADED FROM ver 4.1 to VER 5.0. The obvious benefit is the TMC but I did notice that the voice instructions, especially on roundabouts, were a lot better. Now 5.1 is out have a look on ebay for a ver5.0. The TMC has certainly saved me time on at least 2 occassions.
No definite answer on whats included in VER5.1 - MB Dealer POI is one item and better maps of Norway from another member. However VER5.0 is discontinued so a dealer will only supply VER5.1.
Yes, the screen does say updating or loading when you put a newer version disk DVD in the boot unit - I assumed this was loading the map data into the unit rather than updating anything on the head unit. I guess it could be the Navigation unit software but I simply don't know. I certainly haven't noticed anything change as a result of moving from 4.1 to 5.0 - apart from the Navigation changes.
If you do get the new head unit software let us know if you notice any changes. Obviously you will need the ver5.1 disk to check if the traffic icons are on the correct side of the road.