I've never fallen out of my treestand, but I've had steps pull out of trees a time out two. Luckily, I was close enough to the ground that it didn't matter.

I've rarely, if ever used a pine tree for a stand. I use oaks, hickory's, wild cherry, and some others, but always look for good cover at my stand height. That's why I almost always use a hand-on type stand instead of my ol' man climber.