I started to determine how many skis are registered in the US. I found some statistics from between 2004-2006 from reliable sources that stated the number of registered skis for the areas listed below. Using those areas as a representative sample, I then calculated avg. skis per person. (Sorry, the chart posted like crap)
Location / Total Population / Total Registered PWC / % PWC Owners
State of Utah / 2,233,169 / 14,251 / 0.64%
State of California / 33,871,648 / 159,335 / 0.47%
Miami-Dade County, FL / 1,217,896 / 8,479 / 0.70%
Broward County, FL / 1,623,018 / 7,607 / 0.47%
Average is .57%. x 300MM population of US = 1.7MM registered skis. I thought my data would be skewed since FL and CA are going to be higher than other areas, but because of their higher population (and likely lower income demographic), it seemed about right. It was later confirmed when I found a statistic from the USCG stating that 1.55MM PWC were in use in 2005. So, my guess was pretty close.
So, there are about 1,600,000 skis in the US. Let's assume only 5% of them are standups. That's 80,000 standups. Even if EVERY SU rider had two or three like we do, that would still be 30,000+ standup riders.
Even if we assume SU riders only makeup 2% of the PWC population, that is still 32,000 SU's in the US.