I'm pretty sure we've already reached the point where the security updates are coming faster than my desire to run Flash -- that is, every time I want to play Flash, I have to update it first. Kind of like how every time I turn on my Playstation, I can't actually play any games until it spends two hours downloading updates first.
I guess that's a good sign, coffin-nail-wise?
If you use Safari, ClickToPlugin is decent. It translates many Flash players to HTML5 players, including Youtube.