Went to a Customs seminar on their newer epoxy CEG-Lite and using it on glass tiles. Gee, I don't think I'll ever use anything else on glass now that I seen that. The stuff is awesome and it is the setting compound and grout all in one.
http://www.custombuildingproducts.com/ProductCatalog/Grout/ceg-lite.aspx?user=arc&lang=en
http://www.custombuildingproducts.com/ProductCatalog/Grout/ceg-lite.aspx?user=arc&lang=en