When I fist started riding at the place where I am now, my instructor recommended that I read Centred Riding.
I thought it was quite helpful - there were times that I thought it was a bit to full of imagery and not quite direct enough in what it was saying.
But having said that I recently re-read it and thought that it was interesting that after another 2 or 3 months riding that I was far enough along that I took a completely different message from the book. Its a great read
After reading this thread I have also just bought balance in motion off ebay
and can't wait for it to arrive!!!!!!!!!