It will work anywhere in the world, regardless of where you buy it.
However, a unit purchased from a US vendor will almost certainly have the N. America basemap installed, rather than a European version.
Since these basemaps cannot be changed (except at the factory) you'd have to buy some additional mapping for it. More detailed maps are needed for useful car nav anyway, since the basemaps do not contain much detail.
-Wlw
Thanks wildlifewriter. What do some of these maps cost?