The Kessler Syndrome

The collisions you see in the new blockbuster "Gravity" have been happening and will continue to happen.  

From YahooBlogs:
On February 10, 2009, at just before noon Eastern Time,  a 1-ton hunk of space debris, formerly the Russian satellite known as Kosmos 2251, slammed into the American Iridium 33 communications satellite going over 40,000 km/h. The collision destroyed both satellites, creating a debris field that continues to travel around the planet, and is considered to be the triggering event of what's known as the Kessler Syndrome.
The Kessler Syndrome, is a fairly simple concept, most recently demonstrated in the movie Gravity. Collisions between objects (both man-made and natural) in orbit of Earth will result in a cascade effect of further collisions that will eventually make it extremely dangerous to send anything else into orbit — effectively cutting off our access to space. This great short video talks about the Kessler Syndrome and shows how it progresses: