Hi,
I have created a presentation about the new 6.4.0 with
some (recycled) GRASS + OSGeo intro slides, shown
at the 10th GRASS-GFOSS meeting in Cagliary, Italy:
http://www.slideshare.net/markusN/grass-gis-640
(ODP, PPT, PDF,...)
Feel free to use the material, it is licensed CC-BY-SA.
cheers
Markus