When the rear tire's off the ground, that't when it gets fun.
The steepest I've done would be about70-80 degrees at a place called the ***** Bowl, its about 4m down, it's fun because there is a jump at the bottom of it.
The hardest part about going down steep stuff is what goes on in your mind. Just forget about what MIGHT happen and do it, you'll be surprised, it doesn't hurt much at all when you crash. And if your still not feeling confident, just try and find somewhere open that has a steep hill and ride down it, because here there is nothing to run into.
The most common thing that happens to scared riders is they lock up their brakes, don't do this because you lose control, and that's when you may hurt yourself.