The image above shows the outer casing of an iPad 2 (left) next to what is said to be the same part of an iPad 3.
The differences may not be immediately obvious, but upon closer inspection you can see some of the differences. The logic board mount allows for a larger battery. If this piece is real, that could mean a longer battery life for the iPad 3.
Also different is the camera. Perhaps this will be a higher-resolution camera with a better image sensor. The display will also be different, but it’s unclear whether or not it’s going to be a Retina Display.
The iPad 3 is rumored to be on schedule for an announcement in March with a release very shortly after.