Mapshare is more for changes like roads being blocked, roads being made one way, wrong street names or points of interest in the wrong place. For those kind of things, it works pretty well and I would rather have it than not (- currently up to about 61,500 on my TomTom 910). It was originally supposed to be much more radical i.e. you could add your own streets or roundabouts but these were taken out of the beta (- maybe this'll be improved at some point, I'm not sure).
You do have various levels of Mapshare in the options to decide which user updates to accept (- for example just those which have been verified by TomTom or going to the other extreme those just uploaded by a single user). It's no substitute for having up to date maps though ( the latest being 7.15 which is based on the October 2007 Tele Atlas data).
It's worth having a look at
this link which covers Mapshare in more detail.
Robert
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