In the UK at least there are many roads known locally as accident black spots where there are an unusually high number of serious accidents. It would be nice if it was possible to add permanent marker to show where these locations are. I envisage them working in the same way as speed cameras.
It seems this data is already recorded e.g. http://www.gps-data-team.com/poi/united_kingdom/safety/Accident_Black_Spots-UK.html.
I think the TomTom premium services provide this data as well.