The road geometry may come from TomTom in a lot of areas, but the geolocation information along those roads is not from TomTom. That's a separate layer that Apple is sourcing and applying from someone else.
The level of satisfaction with maps really depends on where you live and how you use them. If you live in the States, well Apple can do no wrong. But for the other 95% of the world's population, the gap between Apple Maps and its competitiors is larger. That's not to say that Google or Nokia Maps don't have mistakes By and large, however, Apple Maps are worse for most of the rest of the world compared to the rest of their competitors. This is not just on the maps themselves, but on POI, traffic info, etc. Example:
I would contend that the Maps are substantially more accurate in the US. Google Maps was like this when it launched. But it has improved substantially for the rest of the world over time.
The other big issue is information and service. Americans drive. Transit usage in the USA is among the lowest in the world. Realistically, outside of commuter service in a few major cities, regular transit usage is largely restricted to the core areas of a literal handful of cities. So Americans will be quite happy with turn-by-turn navigation and don't really care about the lack of transit information. This is pretty much the opposite of what most of the world looks for with mobile map information, where transit information is essential and turn-by-turn is a nice-to-have. Nobody in Houston cares about transit information. But how many Londoners would really prioritize turn-by-turn over Tube information?
But none of this is going to hurt sales so really it's irrelevant. Apple will sell phones. And Apple's most loyal fans are so loyal that they will put up with inferior maps if they have to. They'll even pay for alternatives on their phones or pay for information they used to have (like transit info). Most companies would do anything to have that loyal a user base.
I would stick to iOS 5 untill Google comes up with their Maps app for the iOS 6. Apple tried to reinvent hot water but ended up with having only water.
Filtered, reverse osmosis, 100.00% contaminant-free water.