Maps can be cached. OSM is under a CC license (so even if they die, you could legally set up your own server with their data), and MM can handle GIS maps as well (most GIS servers are operated by governmental agencies, under the FOI act or similar rules, so their data can't get lost over a change of license either). Besides, with that amount of free map data about, even if Google, MS and Yahoo revert to non-free business models, many other services would immediately step in.

The point against Maemo Mapper is another: It is no navigation software, and until something similar to OSM with a focus on routing metadata takes off, it won't be good navigation software, no matter what effort MM itself would make at it - routing without up-to-date congestion rates, construction sites and the like is barely more efficient than following signposts.

Sevo