ETTR - Exposing To The Right - is about setting your exposure such that your histogram right toe touches but does not get chopped off by the vertical right axis of your histogram. This way, you capture the maximum amount of light that your digital sensor and in-camera electronics processing can take. This gives the highest Signal to Noise ratio for your photo.
Above is a 2 MP Nikon 775 shot. The light was "right", you can see good grass colour, blue sky and clouds. Capturing a both sky and ground tones with this camera can be quite difficult - the sky usually gets burnt to white.
Stu Maschwitz of the Prolost blog argues that there is no one blanket philosophy for exposure (dead link). If your real scene is of such high dynamic range that it the histogram is so wide that it spans and exceeds both the left and the right axes, then, you're between a hard place and a rock. You either call it a day or come up with a James T. Kirk solution to the Kobayashi Maru.
Luminous Landscape is a well known reference website for photographic detailers. They have an article on ETTR. Emil Martinec writes a scholarly discourse on Image Noise, Dynamic Range and Bit Depth in Digital SLRs - his webpage is at the University of Chicago.
On the other hand, spotted at the DPREVIEW Sony forum ...