The whole article is worth quoting, but here's a taste:
"It’s easy to see how unbreakable promises would be a revolution for contracts and law. Enforcement costs for contracts would be drastically reduced. It would enable a new era of globalization, allowing people to participate in contracts with each other without regard to jurisdiction. The rights promised to a citizen of a country could be guaranteed instead of relying on the benevolence and caprice of their sovereign."
I hope it stays up - well worth a read.
Edit: it's even better if you read it just before/after reading this thread:
https://bitcointalk.org/index.php?topic=232950.0