We make cabinet glass and and as such we cut most pieces out of larger sheets of glass and do other operations on them that add value. While I know that true virtual products are like downloads, ebooks, etc. I am using it to sell glass panels. I have a template set up here on Sunshop. Click Here
I would rather use Magento as well I just really like the way it works compared to other carts but I need this finctionality.
Magento virtual products let you add a product and then add product options as in Click Here. Since these options can modify the price I thought it would be an easy bridge to insert a script that would take the value from 3 option values (height, width, and sq. ft. price) and then run a calculation to either return this value to the magento price calculation script or return it to another custom option as the value of price adjustment field.