Good article over at Tech Central Station.

I do think he misses a bit when he says,

The other myth found in much of the coverage is that this is a useful technology for spaceflight.

Proponents claim that by allowing airbreathing up to high Mach numbers, there is no need to take along as much oxygen for the rocket engines, because they can gather it for "free." This argument assumes that space transportation is expensive because propellants are, but those aren't the cost driver. If they were, space would already be affordable, because liquid oxygen is actually about as cheap as milk. Propellant costs are such a tiny fraction of launch costs that they're down in the noise. If we ever get to the point where they become a real issue (as they are for airlines), we'll have solved the problem.

The dream that many have for scramjets is that they will reduce the amount of propellant that must be lifted from the Earth's surface, with the hope of greatly reducing the size, weight, and cost of the launch vehicle. It takes propellant to accelerate propellant, so the less propellant that you need to launch, the smaller the vehicle can be. It's a reverse snowball effect, and aerospace vehicles tend to cost by the pound. Take a look at the first stage of any booster in terms of size and weight compared to the second stage. If you could accelerate the vehicle to high altitude and velocity using something like a reusable scramjet powered mothership, then the booster required to send a payload the rest of the way to orbit could be a lot smaller and less expensive. However, creating that hypersonic mothership is an incredible engineering challenge that would cost huge amounts of money. No one is willing to pay for it and it would take a LOT of launches to recoup the development costs compared to building the first stages to lift the same payload.