It is possible to add your own Points of Interest (POI) to the iDrive navigation system. The steps required are documented here:

http://www.bmwnavaddpoi.co.uk/

This is mainly of interesting to add speed and/or redlight cameras to the map, but you can use it to add any entries you want. You can even add your own groups with categories in it.

Restrictions of using POI on the iDrive Navi compared to aftermarket GPS systems:

• Only 1 POI category can be displayed at any one time (the last category you looked at, or searched in)
• No warnings of POI that are on your route (e.g. approaching a speedcamera) other then a little icon on the map
  
• Since you can only have one POI category displayed on the map at any one time, all POI of interest need to be in the same category, and a category can only have one icon. So for speed/redlight cameras you cannot have different icons for different types/speeds of cameras