Japanese people put much more emphasis on "Manner". It's very common for their cell phones to have "Manner" modes installed. This mode is switched on whenever they commute, so that their cell phones don't ring and disturb others. For this reason, they also rarely talk on phones on public transport, they text each other instead.
In Tokyo, I had never seen a girl who didn't wear any make-up, I heard that they think wearing make-up shows respect and politeness. Hong Kong girls are catching up, but there are still some differences. In Hong Kong, girls with heavy make-up may be seen as slutty by other girls. It's also very common to see people bow(90 degrees) when saying goodbye in JR stations. Again, this shows great respects but in Hong Kong, people may think it's weird to bow at 90 degrees.
Another big difference is the relationship between men and women. Girls in Hong Kong are generally more independant and have higher social status. Guys in Hong Kong treat girls better from what I heard. I've also read a newspaper article about the increasing popularity of "Prince Cafe". Waiters there are westerners who treat their customers(mainly Japanese ladies) as Princesses, while Japanese guys generally don't treat girls very well.
That's only my impression on Japanese people, I know they are only shallow observations... Would love to hear from Japanese people who are now staying in Hong Kong.