In the US part of the globe, I think the USGS photos go to 1m resolution, higher if you are in an urban center. Outside, its good enough to make out roads and such, but no real detail.
EDIT: Some Examples, showing the Joe Louis Arena and Cobo Hall in Detroit:
Urban view, only available over big US cities

Same shot, only using the USGS survey photos, available for anywhere in teh country:

Same area, but zoomed out so it wasn't a big blob. Satellite photo, this resolution is available for anywhere in the world:
