Subsantial new infrastructure would have to be built to accommodate person to person transactions. When I deal with an established vendor, I use a credit card almost 100% of the time and while not electronic currency it is close.

When I buy orsell something of craigslist right now it is almost always cash and the infrastructure available would have to change substantially for that to change.

how often do you buy or sell something on craigslist and coins are involved?

Perhaps coins aren't used much on Craigslist, but:

1. Vending machines

2. Giving change to folks on the street

Also, plenty of people, for whatever reason, pay cash at stores; coins are needed there, of course.

And finally: for better or worse, cash is anonymous. Until a dependable replacement that is also anonymous comes along, people won't switch from cash.

nah, coins aren't needed.

cash is in general, but not coins.

From a user perspective, debit/credit cards already fill this niche (is the plastic money culture different in Japan?).

Yes credit cards are more prevalent in the US, but they have a 3% overhead, retailers eat the cost. With value points and clubs you can recover 1-2% of those fees. I think a fee-free anonymous electronic cash system like Suica would be a great alternative.

You can buy and recharge Suica cards at train station ticket machines, so they're effortless to obtain. Having been to Tokyo twice in the past 3 years, the Suica cards are a godsend. I used them only for transportation purposes, but I saw stores that accepted them.

I had a Suica card that I bought the first time I went in 2008. I didn't use up all the money that I put on the card and kept it when I came home as a souvenir. When I returned in 2010, I brought it with me, figuring that there was a time limit on the validity of the card, or that I would have to get the card re-activated first. No, it worked just like it did when I bought it in 2008. When it ran out of money, I went to a Suica-issuing ticket machine and put more money on the card. So, don't throw these cards away.

For what it's worth I just came back from a week and a half in Japan and never knew these things existed (well, I knew there was some sort of smartcard system for the subway I wasn't using, but had no idea it extended further than that). Japan is still the most cash-heavy culture I've visited.

The US, on the other hand, is the most plastic-heavy culture I've visited. It's the only place where it's socially acceptable to pay for a $1.50 cup of coffee with a credit card.

Yeah, you definitely need to have cash with you. Plan on visiting the ATM often while there, especially during Golden Week. The Suica card makes it effortless to travel on Tokyo Metro and the JR lines.

The nice thing about Japan is that you'll never get mugged here. So you might as well withdraw all the cash you'll need during the Golden Week.

(But you should avoid the Golden Week if you're coming from abroad)