These are links to the two companies that send us samples of their landscaping glass. There is a materials calculator here: http://www.thegardenofglass.com/pages.asp?pageid=45023 which suggests that to cover a 10ft by 10ft square with one inch of glass would take about 700lbs. Prices per pound seem to range from $1.30 to $6.00 depending on amount of tumbling.
The glass seems to be visually tempting and certainly lends to the feeling of being in an space outside of the everyday. It appears to be perfectly safe and not too messy. There were concerns mentioned about the sound created by walking on the glass might very grating. Also the price is a concern. There possibility of mixing rocks and glass was also suggested.