Integration of OpenGL VBOs and vertex arrays for faster 3D Viewport rendering
by Lukas Steiblys (imbusy) for Blender Foundation
One of the biggest weaknesses of Blender is the inability to render high polygon counts while modeling. I believe the way blender uses OpenGL API is the biggest cause: it does immediate mode rendering. Using VBOs and vertex arrays, sometimes called the retained mode, would speed up the rendering substantially and provide a user with a more responsive interface.