Heck, I'm not even worried about the speed of a reaction. But remember that if I fall towards the earth, with a force, the earth has the same force exerted upon it in the opposite direction.
I was thinking, after reading a comment on a previous gravity question, that gravity should be propagated by particles (this would explain why you instantly feel gravity, its like entering a stream of particles). This would also explain why it would take time to feel a change in the gravitational field. If the change propagates at c, that would explain how similar gravitons are to light.
Anyway, if I absorb gravitons, why does the planet care? It acts as though it absorbed equal and opposite gravitons in terms of its resultant force experience. Do we state that a disturbance in the field is sensed, rather like a pressure buildup? I imagine in analogy a water buildup when I stand in the shower propagating backwards up the shower head. It seems as though disturbances in the field would explain it, implying virtual gravitons in an analogy to virtual photons perhaps. Feel free to ignore that if I'm mistreating the idea of virtual photons or whatever-I have heard them described as field disturbances though.
To further clarify, an analogy: suppose I am a rotating sprinkler at high frequency. As I throw down water all about me, a post in the garden "absorbs" the water I throw at it. I, however, do not react at all, just the water. However, according to what we observe, a planet reacts to a person's weight, and this in my perspective can only be answered if the planet "senses" when its gravitons have been absorbed and tries to fill in the gap, throwing in more gravitons than before. Since more gravitons are emitted forward, this would explain why the earth feels a forward push, given that gravitons carry negative energy. (Of course they have to have negative energy, otherwise when you get hit by one it would push you away).
This seems more like a fluid force if the fluid moves from regions of low to high density, filling in the gap from absorbant things, in this case all mass-containing objects.
Does this sound ok, or am I totally wrong on a point of importance?