I had a 4.5m boat with a f70 and loved it, put almost 300 hrs on it in the first year before getting an offer I couldn't resist on the outfit so sold it on. The next boat had a Suzuki which I kept for another 12 months before selling once again.
I much preferred the yam f 70 so bought another boat with another. I've now clocked close to 300 hrs again in just over 12 months of faultless boating. Both yamahas gave me close to identicle performance on completely different boats in terms of speed and fuel burn.
My last trip of 130 km used 38 lt of fuel much of which was pushing into quite rough seas. Service costs are the cheapest I've ever had on any 4 stroke and simple to do yourself, though I use a Yamaha mechanic.
I was recently on a tour boat in northern Queensland that was using a pair of f70 which had clocked up 7100 hrs of faultless hours doing daily river crocodile tours. I was told they keep the engines untill they reach 10000 hrs. I also have a mate who was a outboard mechanic who serviced houseboat outboards using a f70 on his work punt. He had clocked over 3000 hrs in two years and was loving his, unfortunatly now passed from cancer.
My only complaint has been that if there's a bit of wind blowing I often can't here my engine running and try to start it when it's already running!!!!.. Love mine and feel confident even on long range offshore trips.