It's quite rubbish in the UK.
Lots of it in black and white or very low-res.
My home town (pop. 25k) is labelled about a mile North of where it should be, and a sub-district of my home town is in the place of the center of my town!
Apple has ALOT of work to do before iOS 6 Maps is anything like the quality of Google Maps.
The 3D Maps in big cities are impressive though - shame I don't live in one.