Gravitons should move near or at the speed of light:

http://relativity.livingreviews.org/Articles/lrr-2001-4/node29.html

To quote:

Predicted in Einstein's General Theory of Relativity, gravitational waves are disturbances in the curvature of spacetime caused by the motions of matter. Propagating at (or near) the speed of light, gravitational waves do not travel "through" spacetime as such -- the fabric of spacetime itself is oscillating. Though gravitational waves pass straight t hrough matter, their strength weakens proportionally to the distance traveled from the source. A gravitational wave arriving on Earth will alternately stretch and shrink distances, though on an incredibly small scale -- by a factor of for very strong sources. That's roughly equivalent to measuring a change the size of an atom in the distance from the Sun to Earth!

No wonder these waves are so hard to detect.

Are Gravitational Waves Real?

The first test of Einstein's General Theory of Relativity (the bending of light by the gravity of a large mass, seen in a solar eclipse) was made by a team led by Sir Arthur Eddington, who became one of the strongest supporters of the new theory. But when it came to gravity wave s, Eddington was skeptical and reportedly commented, "Gravitational waves propagate at the speed of thought."