The Narita police are notorious for their racist harrassment of foreigners. They never stop Japanese for questioning, only foreigners, and they seem to have a quota that they work through. Plenty of evidence that this is happening, and I have seen it with my own eyes.
At least ask them to show their ID, which they are legally required to do, and give them a lecture on racism, which I did last time I was harrassed.
This seems to be ongoing as I noticed a lot of foreigners being harrassed when I was last there in May 2010.
for some odd reason, many teens and 50+ adults knew english but those inbetween seem to struggle. I was in no danger though. I did bring a 50lb suitcase and got tired of carrying it around and left it at the subway to ask for directions up a flight of stairs and it was still there when I came back. You can walk around 3am w/o being worried about rape. Very honest people but you are to visit not stay as they still remember WWII.
Do what the Japanese do, and that's pack very light. On the crowded public transport system there's little space for luggage, and very little sympathy for it too.
In stations also, you'll find that lifts and escalators are few and far between ..
When I went to Japan, I was warned that it is best to wait until you arrive at your destination within Japan to exchange your money. At Narita, they charge you some to exchange your money.
However, it may be worth it to exchange your money at Narita if you are uncomfortable with trying to find a bank elsewhere to exchange your money. Consider these before you leave the aiport.
First of all, try to buy the souvenirs and gifts you want elsewhere in Japan (wherever it is that you travel to within Japan). However, for those souvenirs and gifts that you forgot to purchase or didn't realize you wanted until you came to the airport, I suggest you shop around if you have time. Some of the shops sell the same items at slightly different prices. Also, if possible, try to recall the typical prices of the items you want to purchase. Some souvenirs are pretty standard prices, while others are a bit expensive. Of course, if you won't be back in Japan for a while, and there's something you want, you'll just have to take a deep breath and cough up the money!