I have twin 150 yams, 2006's, I have just over 1300 hrs on each one. That being said I use it for guiding and most likely 80% of these hrs are on the troll. I do my oil changes every 200 as stated in the manual, I changed my impellers at 1000 hrs just because I was worried I would loose one offshore, they were both still in good shape. Gear oil every season, basic TLC and these things are still running like a top. Only problem I ever had was a plugged injector, it was my bad, no in line Racor system, only the bull$hit, cheap spin on. I learned the hard way, had to get four new ones flown into the middle of nowhere to get me home, wasn't cheap.
Bottom line,I think Yamaha's are top of the line, look how many you see around. I would for sure buy more when need, don't think you can go wrong.