Here are some interesting stats from the National Marine Manufacturers Association  (NMMA). 

These are the top ten boating states, ranked in order by total annual expenditures for new powerboats, motors, trailers and accessories in 2009.  (Keep in mind, that does leave a lot of the market out of the equation.)
Michigan, Florida and California have always been tops in the number of DMV vessel registrations but expenditures tell a different story with Michigan down in 9th position. 

Florida ($1.2 billion)
Texas ($906 million)
California ($417 million)
North Carolina ($395 million)
New York ($381 million)
Louisiana ($370 million)
Washington ($339 million)
Delaware ($330 million)
Michigan ($317 million)
Minnesota ($305 million)

Florida and Texas must have some big boats because the gap between them and the rest of the pack is huge.  This definitely tells the old 80/20 story with the top two states adding up to almost the same as the next 8.