(2-part post):
It's certainly a repeat question. I've been a member of AB for about 20 months and there's hardly been a single day when something similar hasn't been asked. Unfortunately, despite all of those questions and answers, your chances of getting into the USA still remain uncertain:
Fact 1: The provisions of the Rehabilitation of Offenders Act don't apply outside of the UK. Unless other countries have similar legislation in place, your conviction will never be regarded as spent as far as foreign governments are concerned.
Fact 2: The US embassy website states that you require a visa. (It states that anyone who's ever been arrested, even if totally innocent, is ineligible for the Visa Waiver Program).
Fact 3: You've no chance of getting a visa within 5 weeks. (It takes up to 6 weeks to get hold of a copy of your police record, several weeks to wait for an interview at the US embassy and anywhere between 8 and 16 weeks to wait to hear the outcome of your application).
Fact 4: The Visa Waiver form, which is completed on the plane only asks about convictions for crimes of 'moral turpitude'. Many travellers with minor convictions can truthfully answer 'No' to that question . However, any offence which would, in the USA, be covered under federal law by the Controlled Substance, Drug, Device and Cosmetic Act (or similar offences under state legislation) is classified under 'moral turpitude'. If you want to try to get into the USA, you'll have to lie on the form.