Basically, until they get legal satisfaction for the judgment, they could make a mess of any business he wants to do in the US or with US-based companies. Any money owed to him by any US company would be at-risk of a claim.
These risks are notably less to a developer if they've incorporated, or are selling the software through a publisher. But for the lone developer, it could be quite the hassle.
Also, though the real costs of pursuing such claims might deter actual action by the patent holder, the risk doesn't go away and the 'debt' resulting from the judgment could be sold to people who have lower opportunity cost and even less moral fiber.
These risks are notably less to a developer if they've incorporated, or are selling the software through a publisher. But for the lone developer, it could be quite the hassle.
Also, though the real costs of pursuing such claims might deter actual action by the patent holder, the risk doesn't go away and the 'debt' resulting from the judgment could be sold to people who have lower opportunity cost and even less moral fiber.