I've been spending a lot of time fixing problems reported by this web site in Minneapolis, of all places. I'd say the most common TIGER import problem is unconnected ways, which no doubt makes routing problematic. I'd also say the most common human introduced problem is unconnected ways, particularly when splitting a single way into two oneway streets.

You owe it to yourself to take a look at where you've been editing from this site. You'd be surprised how many little mistakes might appear.