>>Just to clarify: the last paragraph explains that gravity isn't an attractive force in general relativity, it is motion along curved geodesics. In other words, space-time is warped, and movement through warped space-time is what we call gravity.
>
>Correct. I am still accustomed to think of it as an attraction, though...

I think quantum gravity will eventually put it back to an attractive force.

Also, my thoughts on mass are something like the following:

Mass is a measurement
Mass is a measurement of some fundamental quantity, let's just call it fundamental mass
Photons are what allow us to interact with the world
Photons are what allow us to measure mass
So photons have fundamental mass, but because photons are what allow us to measure mass, they won't be measured to have mass themselves
Fundamental mass is what gravity acts on, not the mass we measure

Just something to chew on.