Credit card acceptance is a lot better nowadays, but there'll chances are they'll be one or two times when you can't pay with VISA/Mastercard/AMEX, so do have some cash in case.
There's probably some better stats, but I'd guess over 80% of restaurants/bar/cafes will accept your cards, and taxis similar. Shops are probably have a much higher acceptance rate.
There's plenty of ATMs that accept international cards now, so you'll be able to get cash pretty easily.
Also (in case you haven't already) check with your bank/credit card in case you need to notify them you'll be using your cards in Japan - some banks anti-fraud departments might automatically stop transactions overseas.