I've been cleaning up a bunch of maplint reported by Keepright, http://keepright.ipax.at/, which rocks!
(All comments based on USA data.)
Unfortunately, I'm starting to get to the conclusion that routing OSM data just won't work for any road smaller than highway=tertiary. It seems that the TIGER import didn't connect a bunch of roads near county lines that are away from the cities. That's not too hard to fix if mappers spend some effort.
There is also a fair amount of bad data due to edits. For example, streets are split into parallel one-way roads, but the new road doesn't get an intersection at every road it crosses. Or the new driveway almost touches the main road.
The trouble is things look good in the web. Intersections are rendered the same as non-intersecting roads. Visually, the map is good enough. However, from a routing perspective, the roads never meet, so you'll never get to make that right turn. This is going to be a serious problem for anyone who wants to use OSM data for routing. Without going to external websites, the map appears just fine, possibly leading to more incomplete edits.
Until this data gets beat into submission, I think OSM maps are going to be good for printing and viewing but risky for door-to-door routing.
So how important is routing?