I actually just got back from Tokyo a month ago, and I have to say it's not as intimidating as you'd think. I only know a very few phrases and some basic customs, so you don't have to be an expert by any means to survive in Tokyo. Everyone is extremely polite, and as long as you have a guide book with phrases you'll be fine. The only problem I had was getting my subway card creased and having to call the operators over to give me a new one. I was also amazed at how cheap things were, considering how much you usually hear about Japan being expensive.
For anyone going, be sure to hit Akihiba
