Well, let me put in a few counterpoints, with links, so you can make up your own mind.
Pleasure, Tourism, Medical Treatment - Visitor Visas (B-2) - If the purpose of the planned travel is recreational in nature, including tourism, visiting friends or relatives, rest, or is related to medical treatment, activities of a fraternal, social, or service nature, or participation by amateurs who will receive no remuneration in musical, sports and similar events or contests, then a visitor visa (B-2) would be the appropriate type of visa for the travel. Persons planning to travel to the United States for a different purpose including students, temporary workers, crew members, or journalists, must apply for a different category of visa.
http://travel.state.gov/content/dam/...2014_print.pdf
Also check out this link, particularly the first bullet on page 2. (For some weird reason I can't copy&paste.)
http://www.eandvh.com/engine/pubs/ge...spx?id=40&dl=1
There's a lot more discussion on this in the "JAA PPL in the US" thread, particularly on the last page (page 5):
http://www.pprune.org/private-flying...-part-1-a.html