I'm not optimistic that scramjets will ever power airliners, breathless news reports to the contrary. You can't ignite a scramjet until you're going extremely fast. Ignition speed depends on the specific scramjet design, but Mach 4+ is a commonly mentioned velocity.

A typical flight profile would use turbojets or turbofan engines to take off horizontally and to accelerate to somewhere around Mach 2.5 (faster than the Concorde's cruising speed). You'd then transition to ramjet power to accelerate to the scramjet ignition speed, then accelerate to the cruising speed. As you approach your destination and want to slow down, you'd first throttle back the scramjet until you're back around the ignition velocity, then transition through ramjet and later turbojet power for landing.

Some of the problems with an airliner using this approach is that the turbojets represent a lot of dead weight during the cruising phase of the flight. There's also the matter of heat. Crusing at Mach 3.15, the SR-71 Blackbird got very hot. When coming in for a landing, they'd sometimes orbited at about 40K feet at subsonic speeds to let the airframe cool. They also had to have special handling procedures on the ground because it was still very hot. A scramjet powered airliner going twice as fast would get extremely hot, so things like deplaning the passengers and unloading luggage could prove challenging.

It's possible that scramjet technology could be used to create a reusable "mothership" for spacecraft. This idea is discussed in the Nov 1, 2004 issue of "Aviation Week & Space Technology." They propose developing a Mach 7 version first stage (kind of like a larger and much faster version of Rutan's "White Knight") to carry the second stage that would fly into orbit. Their goal is to put up to 20,000 pounds into LEO. It's a pretty cool idea if they can get the funding. I don't think the first stage would need to be manned, and in fact, that probably wouldn't even be desirable. If they develop such a vehicle, they might eventually develop a manned version of the 2nd stage. If that happens, then yes, scramjets could be used for manned flight, just indirectly. I hope it happens.