I've heard some debate on the mailing lists about whether importing TIGER census maps into the US was a good idea. The con argument is people look at the map and figure it's good enough. The pro side is it put a lot of useful data in place.
Unfortunately, the quality of the TIGER data needs some improvement. For one thing, the highway= tag does not cover much ground between residential and motorway. There are lots of preferred roads, especially away from the cities, and you can't just look at a TIGER map and know which one to take.
I've been applying the highway=tertiary tag to lots of the backroads in Oregon. One thing I particularly like finding are roads that have been re-routed (which is a really neat thing to look for on old maps). Take a look at the underlying Bing! image and see how Seven Mile Hill Road used to take a bit of a meander to the south.