Because there's no such thing as the suspension of disbelief anymore, some party-pooping physicists (links to PDF of actual paper) took the time to prove that, while Batman could jump from a height of 400-feet and successfully glide for about 1,000 feet, he would land like a sack of shit thrown at a neighbor's porch. Whatever -- you don't know what kind of magic Lucius Fox packed into that cape!
In a paper titled "Trajectory of a falling Batman," David Marshall, Tom Hands, Ian Griffiths and Gareth Douglas studied the wingspan, height of descent and velocity representative of Batman's cape during one of his flights. As part of their research they exposed the bat cape's fatal flaws.
While this is enough to support a glide of sorts, according to the team's calculations, the essential accessory falls short. The 15.4-foot wingspan is only half of a hang glider. If Batman launched himself off one of Gotham's average 492-foot high towers he could glide successfully for approximately 1,150 feet.
The problem is the caped crusader's velocity would peak somewhere around 68 mph before leveling off at 50 mph -- enough speed to cause Batman to take a permanent dirt nap upon "landing."
Gee guys, thanks for proving something in a superhero movie isn't possible. Really. Maybe next you should tackle whether or not it's possible to suck all the fun out of something. Note to all readers: Do NOT go see The Dark Knight Rises with these @$$holes.
Thanks to towo and ashleigh, who can't wait to hear their explanation about how superheroes wouldn't really be able to breathe in space.