Since Apple released iOS v6 and the new Maps app with it, the iPhone has not been a very good helper when you need to find your way around. While many of the trips I've navigated with the iOS Maps have worked out fine, there were at least two different occasions where my destination as directed by Maps was far from the actual location.
In Kowloon Bay while trying to find my way to Miele, Maps took me to a location a full two blocks away. I had to walk the distance because I had already parked my car believing that Maps was accurate. whoops!
In Cheung Sha Wan where I had an interview with a group of middle-school students, Maps took me to a location three blocks away from the actual location. Again, I had to walk the distance because I wasn't driving that day. I arrived 20 mins late for the interview as a result.
Maps is definitely not great in Hong Kong. There are multiple problems with it in general.
There are no street numbers in Maps so you can't locate a street and then identify which block your destination is in.
Building names are extremely important in Hong Kong but Maps doesn't know/display them.
MTR stations are important in Hong Kong but when clicked, many of the MTR station icons in Maps display information about the MTR line that the station is part of, but not the station's actual name; for example, "Mtr-tsuen Wan Line_kcr-west Rail Line" (I didn't make that up!) instead of "Sham Shui Po".
Apparently, Maps is using data from Apple's partner TomTom. You have to wonder how reliable (or not) TomTom's own products are.
But the problem doesn't apply only to Hong Kong. In Australia, people have been stranded in extremely remote areas of Australia while following directions given by Maps. A screenshot on AppleInsider's site demonstrates the problem quite nicely. The situation has occurred so many times that the Australian police have issued an official warning against relying on Maps! WOW!
So if you plan on using Maps and you're strapped for time, or arriving in the wrong place might be life threatening, don't rely on Maps alone. Get another app, or maybe consider getting a traditional hard copy street directory, what we in Australia used to call a 'refidex'.
Cheers all :)