Living in Tampere and in the beginning of the learning curve of OSM.
I have used GPS tracking occasionally to store the logs when needed (exercise or car trips etc.). OSM certainly motivates to keep logging, as I can use the resulting maps with my own exercise logs and route plans as well.
I have already noticed a tendency to select non-tracked routes, even when it means a slight detour.
Mainly Tampere and surrounding areas. I try to keep the tracker running while driving (which is quite a lot), but probably not going to start systematically filling in the blanks. At least not until the basic routes are mapped.
Nokia LD-1W and Nokia N800
Also running Maemo Mapper on the N800 to save the tracks.