I did a tandem jump from upstate NY a few years back.
Best experience in my life. Well except when I first met my wife...
Anyway, I jumped from a height of 11-12,000 feet and free falled for almost 10s.... That is the absolute best part. And because we jumped with a cameraman, when my guide pulled the cord, it took another 2s for the cameraman to drop into a pin and disappear from sight. That's when I realised how fast I was falling... OMG.
Absolutely best thing I ever did in my life. Fun, exciting, and if it weren't so expensive, I would certainly do it again.
As for how dangerous it is... yeah. It's not the safest thing in the world. But you only live once, and I think it's probably more likely that we will die from being rear ended than from your chute not opening.