Depends entirely on how the data is being used, what set of data they're using and so on. I've found that Maps is fine for driving instructions in my area of North East England, but that Walking directions are occasionally missing or not quite right.
Possibly could have done with being more clear instead of a quick reply.
The Maps application probably does have some flaws, but it seems a lot of the flaws are coming from it's mapping data that's stored. This is why buying TomTom wouldn't improve the situation, as the data set itself is where the issue is. In response to ZeroGravitas' statement that TomTom would have noticed before it does depend entirely on how the data set from TomTom is being used but that doesn't necessarily mean that the application is flawed, it could indicate that the data points they've been supplied with aren't consistent for what the application is trying to do.
Apple has made a mistake though, ZeroGravitas is bang on about the buck stopping there. In the UK however we're seeing all sorts of mapping data glitches causing the issues, rather than anything on an application specific level. But it's still Apple's fault, but I stand by the point of them buying TomTom not helping the bail out the boat they're in.