Two satellites collided in orbit two days ago, creating a spray of debris that will have to be closely watched to avoid further collisions. One satellite was an Iridium, one of the 88 or so in orbit (I see it was #33), and the other was a non-functioning Russian Cosmos satellite. I hope the Cosmos had either ejected the nuclear reactor that some of them use or was non-nuclear. I see another nuclear Cosmos had a problem recently. What's interesting about this collision was the height: at 490 miles, the debris is fairly high enough to have some significant lifetime. As debris densities increase, chances of collision greatly increase, greatly increasing debris densities, increasing collisions, which... you get the idea. These sort of things are really bad for our near Earth environment.
Here's a graph of the two orbits. It was a bad high energy collision.
UPDATE: Animation of the two satellites colliding (in a virtual sense).