I actually don't have, and have never had, a facebook or twitter account. So, if I ever try to go to the US it's likely that that will be seen as "refusal to cooperate"? And I'm likely to be denied entry because of it?

Wow.

I don't know what would happen there. If you can convince them that you truly have none, you should be fine, but they may be hard to convince. Immigration officers can refuse non-citizens entry for almost any reason.

I'm the same, may be we would be advised to create a Facebook and Twitter account, but then would you be required to keep updating it and actually using it?

I've had one for a long time, but I don't post publicly. Without friending me, it's difficult to tell that the account's in use.

Does this actually apply to US citizens at all? All the reporting I've read suggests this is solely visa applicants, which of course will never include US citizens.

I don't think there's any official policy, but nothing stops them from asking when you go through customs. It's rare but it happens. For example: http://www.nbcnews.com/news/us-news/american-citizens-u-s-bo...

This US policy doesn't apply to US citizens, but there is nothing to prevent non-US countries from reciprocating and requiring social media accounts from US citizens as part of their visa processes.

> For US citizens, they may hassle you a bit but they have to let you in.

This does not apply to U.S citizens. The very first paragraph of the article covers this.

This specific policy does not apply to US citizens, but the general act of being asked for social media passwords and similar certainly can.