Via Clark Lindsey, here's an interesting first-hand description of what it's like to pilot SpaceShipOne.

I was amused at this part:

We talked about G forces on Tuesday. He says that he gets hit with about 3Gs kicking him backwards as soon as he lights the rocket motor. He's supersonic within about 9 seconds later. But he immediately starts to pull up into an almost vertical climb. So he also gets over 4.3Gs pushing him down into his seat just from that maneuver. The combined force is "very stressful" and Mike says it's "important not to black out" at that point.

Emphasis mine.

<writing in my notebook>

"important ... not to ... black ... out."

Got it. Thank you, Mr. Lindsey.