[swamp40]

I think that's a debatable topic.

Some say it is just a pure geometric effect of curved space (and thus instantaneous), not a force of nature that propagates.

[danbruc]

http://en.wikipedia.org/wiki/Speed_of_gravity

[wiml]

The pure geometric effect propagates at light speed also (unless you want to discard relativity).

[chrischen]

Then we can tug on gravity to send signals instantaneously!