I've seen quite a few rivnut failures on frames, all of them aluminum and carbon. Habanero Cycles welds the bosses to their titanium frames. Makes a ton more sense. I love the ride of ti, rides like a top end steel frame. I did find that I prefer the ride when the frame is mated to a steel fork. Carbon forks are not to my liking as they seem to be a bit too stiff.
Ti is king, for sure! Won't rot, scratches are no biggie as they can be rubbed out quite easily, and weight is more than light enough for a non-pro rider.