Kopeikin and Formalont claim to have measured the speed of gravity in 2003
. This finding has been challenged by several scientists [including Steve Carlip], but, Kopeikin has vigorously defended the study [e.g., http://arxiv.org/abs/astro-ph/0311063]
. The newtonian view was the speed of gravity is infinite, but, I doubt any mainstream scientist takes that seriously anymore - albeit some 'fringe' personalities [e.g. Thomas van Flander] have argued the case. I don't recall anyone claiming it was slower than light.
PS Yes, I intended the observable universe. I tend to refrain from invoking the unobservable universe[s]. The important point here is that gravity, like light, permeates the entire observable universe, hence some amount of spacetime curvature is present everywhere in the observable universe. While it is obviously miniscule in intergalactic space, the extent of curvature is irrelevant within the context of this thread.