I replaced the whole front end except the A arms and steering knuckles last weekend. Then I had an alignment done. Now when I turn the car on (and I assume when the power steering gets pressure) the wheel jumps about 1/2 inch. Is that normal or a sign of impending doom?

That should be normal, when you turn the key it unlocks the steering wheel.

completely normal,no power sterring does it too if the wheel is locked.

Never did it before, and the wheel wasn't locked. This is after you turn the key one notch to unlock the wheel.

If the pin in the steering lock mechanism is pushing against the lock sprocket it can still(HOLD)the steering wheel in place.Turning the key will (release)the wheel.Ive noticed that with my car many times.

If it turns the same direction every time, no matter what position the wheel is in you could have a problem. I would go back and have the alignment check again. and tell them you want to see SAI and included angle too.