I'm gonna add to that 'not for the feint of heart' line. Install a couple linux systems like Debian, Gentoo, or Arch, and it's like riding a bike. It just comes to you after that, so try out Archlinux. It's my personal favorite, and I'm running it just fine on my Macbook. Read the new user guide, and spend the time to experiment and make a system that just works for you. If you're worried about stability don't enable the testing repos. Flash is as simple as pacman -S flashplugin. Actually I think it's time to install Gentoo in VirtualBox and see if I want to switch back to my old love.
Arch is excellent, and seems to have gained a lot of visibility/users in the past few years. And it's a great way to learn. But it is not for someone who says Ubuntu "has started releasing software a little closer to beta than I am comfortable with." Arch will look like the Ubuntu alphas. But you'll learn how to back out of and work around bad upgrades, and usually things will shake out in a few days. Doesn't sound like what you're looking for though.