Tucker summed it (Bikini, Marshall Is.) up well, but let me add a caveat or two.
A few years ago, and this yet may be still the case, there was a limitation on vessel age: 20 years.
Also, a safety inspection by Det Norske Veritas or American Bureau of Shipping was a requirement. Not cheap.
Keith_Angler, a topic brought up at the 2003 FYBA Law Seminar was the California interpretation of foreign-flagged vessels. If no import duty was paid, and even if possessing a cruising permit, yachts were getting pinched for the duty anyway.
One owner--who irately paid-- took the state to court and, after a year or so, managed to get most of the duty back.
Your local Marine Documentation people generally keep up to speed on this sort of 'government assistance'.