I've got a 21' Parker w/150 Yamaha 2 stroke. Close to 600 trips and @ 1800 hours on the engine. It has not failed to start and take me where I want to go and back once in all that time. I am meticulous on maintenance and outside of that the engine has never needed an unscheduled repair. I tried my best to talk the dealer into giving me a Honda when I bought it as Yami did not make a big 4-stroke at the time. Am I glad now that they wouldn't listen to me.

(I had a Yamaha 4stroke and used their "ring-free", and I can tell you it makes a hell of a difference!!, I would not have belived it but that stuff is magic)[/QUOTE]

I was waiting for someone to mention the "ring-free". The stuff is amazing. I ran one season on my Yami 4-stroke without it and had fouled plugs twice. I always run 89 Octane. Last year I ran the ring free with every gas fill-up and the motor ran amazingly better. I do not know what the stuff does but it's great and I would never run without it.

I have a Yamaha 150 four stroke on my 21' CC ; bought it new with the boat in 2004.
Motor has been absolutely perfect- never a single repair ! It starts up every time, and has never failed me. I do bring it in every year to have professionally checked/winterized, and have done preventative recommended maintenance ( water pump change, tune ups, etc ).
As others have stated, it is very quiet in operation and is great on gas.
I don't think you could go wrong with this motor!