If I host a website that has user accounts in the US, and do not stop people from the EU from registering, do I, with no offices outside the US, need to do something different because of this ruling?
If your user is submitting their own personal information to servers outside the EU, that's their lookout. That's what seems to apply to you. Carry on. Nothing to see here.
But if they're submitting to one of your nodes within the EU, they can consider that the data will continue to benefit from the protections being in the EU affords it. Moving it to the US without their permission does not abide the EU protections.
Then (from the company's perspective) I've accomplished the same ends, at a cost to the user (latency), and gone from illegal to legal.
That seems pretty ridiculous.
This would perhaps include deleting data that customers ask you to delete, not storing personal data without direct permission, nor when you no longer need it to provide your service, etc.
> For the purposes of this Directive:
> (a) 'personal data' shall mean any information relating to an identified or identifiable natural person ('data subject'); an identifiable person is one who can be identified, directly or indirectly, in particular by reference to an identification number or to one or more factors specific to his physical, physiological, mental, economic, cultural or social identity;
http://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELE...
This only comes into effect if the data is at any time stored within EU jurisdiction.