A new compilation is available at graphicall.org, with a preview of the new GLSL visualization system. This is an ongoing development project supported by SoC 2007, and will be a great addition to Blender. But what`s this project about? The goal is to improve the display of materials in the 3D View.
The compilation has been provided by Lguillaume, at graphicall.org. You can download it here. Just remember to activate the GLSL preview in the User Preferences Window, at the System & OpenGL tab there is a button called GLSL Preview. You must activate it to use the preview system.
If you want to know more about this project, visit this web page which has all the information about the development. Visit this thread at Blenderartists, to view how some users are using this new tool.