Germany?

[JAJ]

The bad thing is if you had to pay tax even when working outside the country, and maybe to both (or more) nations. I think the UK works like that, no? Or is it the US...

The United Kingdom does not work like that. The United States does, although there are foreign income exclusions and foreign tax credits.

Does Germany work like that?

As far as I know the only major country that imposes tax on non-resident citizens is the United States.

[Christophe]

As to whether you can leave the U.S. to return to Britain, and then go back to the U.S. on a different passport. In theory you can, but your details are logged based on your name, birthplace and if the Immigration Officer discovers you have only just left and are returning on a different passport, you may be due for a "difficult" conversation.

And don't forget the fingerprints, which are also likely to throw up the fact that you are the same person who has only just left the USA.