Prior to Blender v2.67 the default UV map was a square bisected diagonally. In v2.67 the default UV is only the square - no diagonal bisector. Why is that?
By “bisected diagonally”, I guess you mean triangulated? If so, you only need to triangulate the model in edit mode (CTRL+T)
Hi Zafio,
Yes, the square is cut into two triangles.
Actually, I made this observation while following a tutorial; Wireframe in Cycles by Greg Zaal, and specifically at around 05:57 Greg shows a “triangulated” default reset UV. He was using Blender 262.3. Using v2.67 only the square - no triangle- was seen. In either event; triangulated square, or quad, it doesn’t seem to matter very much for the wire shader… or anybody else - just another one of my dumb questions 
Suzanne has some triangles in her, that’s why there are those “bisects” in the ‘Reset’ unwrapping. UV faces correspond in shape to real faces: quads for quads, triangles for triangles, etc.
EDIT: thus, they’re no bisects at all, just edges of triangular faces 
Hey Stan - thanks!