Yes i think its fine, as long as you arn't training. Also you can get an FAA licence issued on the basis of your JAA PPL free of charge....well it would be but the our good old CAA charge £15 for sending the paperwork to the U.S.
The USA is an great place to build hours, new aircraft, GA freindly, No landing fees, free car hire, decent facilities, good weather and briefing services and you get treated like a customer rather than with the contempt you get from some of the airfields in the UK.
I went a couple of years ago so the rules may have changed a little bit but i still dont think you need a visa for flying holidays.
