using gypsum in clay and silty soils

Hi
does anyone have experience in using gypsum (calcium sulphate I believe) to improve the structure of clay soils?
If yes in what quantities is it advisable to use it and how often?

Do you think  it can also be used to improve silty soils?
Thanks
Antonio

the best thing for any type of soil is more OM...

(organic matter)

A quick Google search led me to this informative link about gypsum and clay soil:
http://www.puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/Myths/Gypsum.pdf

We dumped scrap drywall (the kind without fibers) in a low spot on our smal acreage, but after reading part of that PDF file, I probably won't do it again.  Our soil has pockets of clay, but is real alkaline, plus we're on well water.  The last thing I need to add to our soil (plus water) is more calcium.