In 2010, we had a lot of trouble with barnacles growing on Scream's propeller. We cleaned Scream's bottom about once a month, and every time we spent fifteen minutes knocking barnacles off of the propeller with a chisel.
So we decided the try propspeed. Propspeed goes on with a spray gun and hardens to a gelatin-like coating. We paid about NZ$100 to have our 18", three-blade propeller coated.
This is four months growth. The blades are mostly still visible and most of the growth is soft.
We are thrilled with the results. Propspeed keeps the propeller clean. We went from cleaning with a chisel every month to wiping the propeller with a cloth a couple times a year. More importantly, as the propeller is cleaner on average our motoring speed is up about 10% at the same engine RPM.
Scream highly recommends propspeed. Try it, we think that you'll like it.
Update 2013: Almost two years in and the propspeed is still working great. One thing that we did not figure out on our own is that propspeed reduces electrolysis. The propeller is most of the surface area for submerged metal on most boats. Coating it in a non-conductive material makes a huge difference. Our zincs are also almost two years old and look great. We used to replace them more than once a year. Even if a faster boat with less work doesn't impress you, we figure that propspeed pays for itself by reducing the corrosion of your sacrificial zincs.