I've made two so far... my first one has been documented to some degree here:
http://otherpower.com/20page1.htmlIt worked well for the first 9 months or so and produced lots of energy - in fact I never turned it off except to just show that 'it could be turned off' even on windy days when gusts were exceeding 80mph. Then we got an extreme wind event, with gusts (nearby anyhow) exceeding 100 mph and the blades struck the tower.
So I repaired it and ran it again for a while - blades struck the tower again.
About a year and a half ago I took the blades off (to use on another machine) and replaced them with some blades off an old Jacobs machine (I cut them down to 20'). These blades behave well, but they're somewhat narrower and they do tend to stall in higher winds. Since then I've pretty much not turned it off though and it's still producing plenty more energy than I usually need - so i probably will not fit wider blades to it again.
The other one has also been well behaved - it's been up for a year and a half now with no problems. However - as I said originally, to do it over again... I would use a larger bearing if possible. I would also improve the yaw bearing/yaw spindle setup - mine has shown significant wear over the last 4.5 years. A machine this big... many would say - should have some sort of mechanical shutdown. I have no problem shutting down by shorting the alternator - even 1 phase shorted will shut it down in any wind that I've experienced and it will not startup, however, it two wires broke it'd be a mess.
Overall though - the two I have made have served well. Both machines are in the mountains - it is turbulent, I cannot say how they might behave somewhere that got high, sustained winds (we don't see that much around here - we turbulent wind and extreme gusty conditions sometimes).