Very interesting:

The small asteroid Itokawa is just a loosely packed pile of rubble that collected after a collision between asteroids, according to a slew of new studies based on data from Japan's Hayabusa spacecraft. The asteroid appears to be plagued by recurring impacts and tremors today, making its continued survival a mystery.

Hayabusa made two attempts to collect samples from the 535-metre-long space rock in November 2005. The attempts appear to have failed, but that will not be clear unless the spacecraft can be returned to Earth, which scientists are hoping to do in 2010. But during its approach, the spacecraft did take images and other data on Itokawa's topology, composition and gravity field.

According to the article, the asteroid is 40% porous, compared with a handful of sand which is about 20% porous. Over time, one would expect that it would have collided with other objects, either breaking it apart or condensing it together. It's current form seems highly unlikely.