Saw this on boingboing:
Deborah Davis in Denver, Colorado is being prosecuted for refusing to show ID on a bus.
The case is complicated by the status of the bus, which while available to the public is run by a Federal government office complex, and runs through that complex.
But leaving that aside, what is interesting is that she was always OK when she said she didn't have ID, she was arrested (on a later occasion) when she said she had some but wasn't going to show it.
The US, like the UK, doesn't have a compulsory ID card. That means she was practically OK claiming not to be carrying ID - the problem came when she (bravely, and admirably) made an issue of it by admitting she happened to be carrying ID, but refusing to produce it.
This story is the perfect answer to the "we already have so many IDs, what difference does one more make" argument. It is the difference between "I am not carrying ID" and "I won't show you my ID", which the police in this case, typically, considered so important.
(Of course, technically the government claim that the ID cards they are introducing will not be made compulsory. If you believe that...)