[DanBC]

But see what the US embassy in London says: http://london.usembassy.gov/niv/add_crime.html

> We recommend that anyone who have ever been arrested and/or convicted of an offense apply for a visa. In cases where the arrest resulted in a conviction, the individual may be permanently ineligible to receive a visa and in order to travel, a waiver of the permanent ineligibility is required. The Rehabilitation of Offenders Act does not apply to United States visa law. Therefore, even travelers with a spent conviction are required to declare the arrest and/or conviction and apply for a visa.

Imagine you've just spent £X00 on a ticket. Would you gamble that (and the cost of flying back if denied entry), and your future chance of entry to the US, on getting through US border controls?