Larry — you're awesome because you're here a lot and offering plenty of good info to folks' questions. Thanks for being a resource.
>>few people have this issue
That's just inaccurate. I just started having this problem, and one quick google has brought up tons and tons of people asking about it over several years.
>>duplicates in iPhoto are strictly caused by user actions importing things multiple times or other user errors like importing one iPhoto library into another one (which should NEVER be done)
You keep saying that (I've seen your answer on other threads too) — but it's just not true. Maybe wishful thinking. I, for one, have never done either of these things. I always import only once, and delete those pics from the camera. I have never imported another iPhoto library. I've never used any other photo management software. I've never had Photo Stream turned on.
Nevertheless I now have a ton of dupes, and many thumbnails randomly appearing in my library as if they were regular photos. In my case it's especially weird because I'm getting multiple sets of duplicates, and which pics get duplicated seems to have nothing to do with whether I've edited or exported them to Facebook or anything like that — most of the dupes are on photos I've never even looked at since importing them from a phone or camera.
Anyway, I've seen the advice to try various tools and I'll do that. But I just wanted to point out that there is, in fact, something wrong in the iPhoto system. It's not user error. Hope Apple keeps looking at it as an issue to fix. :)