Besides 7-11, Citibank and the post office ATM's, some of the Japanese bank ATM's in touristy areas (eg. Shinsei bank in/around Roppongi Hills) accept foreign ATM's, usually with better hours than the post office.

You will need cash in Japan. Lots of places I go to (e.g. 100-yen stores e.g. Daiso, low-end restaurants, fast food, convenience "combini" stores e.g. am/pm, familymart, Suica/Passmo recharge machines, train ticket vending machines etc) don't take credit cards.

Well, you can live on credit cards in Japan so long as you don't mingle with normal people (i.e. eat at nice restaurants, shop at nice stores). You *can* recharge a Suica with a credit card but it can sometimes be difficult to find a ticket machine that takes credit cards. Most JR stations have such machines, I think, but the subway is basically cash-only.

The other thing that might trip you up is taxis. I have always had trouble getting foreign cards to work with taxis. (Then again, I have trouble getting cards to work with taxis in the US as well...)