How much has Earth drifted (inwards or outwards) from its orbit about the sun? Or has Earth has not moved at all, compared to, say, 1000 years ago? 10,000 years ago?
The mean radius of the earth's orbit has not changed perceptably in the last 1000 years, or even in the last 10,000 years. In the long run, though...
The dominant mechanism in the long run is the solar wind, which is estimated to cause a mass loss of 7-9 x 10^-14 per year. As solar mass is lost, conservation of angular momentum causes the earth's orbit to expand. Obviously this doesn't affect things much in the short run. In the long run, the earth will spiral gradually away from the sun as the sun's mass decreases. About 7 - 8 billion years from now the sun will have lost nearly half its mass, and the earth's orbit will have expanded to roughly 1.5 times its current value.
According to http://arxiv.org/pdf/0801.4031v1.pdf, for several billion of those years the sun itself will have begun expanding at an accelerated rate as it enters its red giant phase. As it expands, it begins to exert increasing tidal forces to retard the earth's orbital velocity (slowing its orbital expansion and allowing the expansion of the sun to catch up), and at about 7.59 billion years the expansion will engulf the earth, which will then enter a decaying orbit and plunge to its Wagnerian doom.