I'd like to know that too. I mean Xero has offices in the US certainly, so they'd be able to be served and the sort, but what about NZ exclusive shops?
So the scenario is that a company in NZ distributes software using NZ servers to users in the US? I can imagine some problems. What happens if they sue the users in the US? What happens if they go to ICE and have the domain you're distributing from seized? What happens if one of the company's officers goes to the US on vacation and gets served?
I guess there's one way to find out. But it seems like the better plan is to fight to eliminate software patents everywhere instead of pretending the internet is going to respect every nation's borders or vice versa.