When I look at our map here in Germany, I see at lot of astonishing spots where a lot of detail is available. On the other hand, there are still many white spots.

So I tried to estimate how many contributing members our project needs in Germany to get a good 100% coverage in the foreseeable future.
Germany has a size of 357021 km^2 and about 82 million inhabitants (from baby to old people).
Now let's assume that somebody can map 20 km^2 i.e. an area of 4 by 5 km without dedicating all his spare time and the rest of his life to mapping. ;-) It may be less in big cities and more in rural areas with only small villages, so I think this evens out. (4 by 5 km sounds reasonable to me. I'm involved in a larger area, more like 8 by 10 km, but didn't and don't have to do everything there myself, luckily.)
This means we need about 18000 people mapping for OSM in Germany or 0,02% of the total population.
The OSM statistics for today say there are currently 28613 users in total.
I don't know, doesn't sound like too many people are needed, but can we reach enough who are both motivated to take the work of mapping AND can handle the technology, i.e. using some GPS capturing device, uploading to the PC, using the editors?
What do you think?