Well there are already portions of space that are expanding faster than the speed of light relative to our position. (see cosmic horizon). The CMB is not just a glowing heat somewhere far away, it's everywhere in the universe in every volume of space. The moment when every point in space (on a Planck-lenght-scale i guess) will be expanding faster than the speed of light relative to one another, than space-time itself will rip apart and that's the end of our universe - at least that is what the Big-Rip theory proposes.