Japan's Yen (円 or 圓) only switches from coin to paper currency at ¥1000. That's $12.50 USD or possibly 15 coins!
I hate coins. I've traveled through the UK (The Pound/£), Europe (The Euro/€), Australia (AUD/$), and New Zealand (NZD/$), all of which have one and two denomination coins. They drive me insane.
My first train ride ever backpacking, I received £18 in £1 coins. (Luckily, my CouchSurfing host was nice enough to swap with me.)
While hitchhiking, I give my rides my loose change. It isn't because I feel the need to pay them. Though it may have seemed like a nice gesture, it's because I hate coins!
When you're city backpacking, nothings worse than a pocket full of rattly change. It makes one leg extraordinarily heavy, and you're always afraid they're going to fall out.
To make things even more confusing (and possibly costly) the Aussie $2 coin is their second smallest. I found so many of them by the roadside, I was in the black for a few days in Oz.
Before you go preaching false economics, look at the numbers. In the US, it would cost citizens more to switch to dollar coins. The only benefactor would actually be the government, The US Mint. This is due to what economists call The Piggy Bank Effect. In essence, coins suck so much, no one wants to carry them. So, people put their coins in a piggy bank or coin jar.
A currency's worth is variable to how much of that currency is in circulation. The more crappy coins in jars, the more currency in circulation, the better for The US Mint, the worse for us.
So yes, we really need to switch to the metric system, and yes, we should lesson our military spending. But for the love of In God We Trust, I hope coin dollars are a long way off.
And if you happen to have a coin jar lying around estimate your net piggy bank worth and leave it in a comment below, or use it to back me on KICKSTARTER!