From a consumer perspective, it was virtually painless. The biggest change is that credit card transactions now require a PIN (assuming a chip card and chip-enabled POS).
The lack of chip card support in Coin effectively makes it a US only product at this point as most of the card-heavy countries have moved past mag swipe (or, are in the process).
Also, as other people have pointed out, the US is moving to chip cards in a couple of years (2015). So this product already has a very short shelf-life.
Once a quarter of cards sport chips and a quarter of machines support chips, it's just a question of issuing new chip cards when old cards come due (or get lost/stolen).
The Chip and Pin machines have a channel to swipe. There are very few places where you hand over a card. For example, in the train stations, the machine to swipe a card is on the same side of the glass as the customer. The agent never handles your card.
So they might be more accepting of Coin (given that they don't see that it is different) than American businesses.
It's entirely possible that Coin may still be useless outside the US if most machines will reject your card's strip.