I hear you but seriously, my instincts after years of troubleshooting this kind of crap is that the problem is the plug-in itself, not the particular developers that use it. I've seen bad javascript, hell I've seen HTML that can cause performance problems. What's happening with flash seems to be related to the underlying technology.

Some users are affected far more than others, and I have noticed very little correlation between particular sites and performance problems. The only constant seems to be: if the site uses flash (and most sites do), there's a high chance browser CPU usage will spike to 90%+ and stay there until it is killed. I think it happens less-often with firefox only because I've got adblock set up and it stops a lot of it from ever being loaded.

I really don't think the symptoms would be like that if this was simply a case of developers misusing the platform. Some sites would rarely have issues, others would fail all the time. It's mostly a gut instinct at this point and I could be wrong, but I don't think so.