well, here's something we've never done before. We got a batch of big pieces of glass from a neighbor, and after much deliberation about how best to place the windows, Melissa decided we needed to cut the windows to the size of the opening (I had thought we might bury parts in, or leave glass up into the wall above for easy building).
So, we had to find a flat surface big enough to hold the glass while we were cutting it. Of course we don't have any full sized pieces of plywood around, so we took a 3 inch foam piece and put it in the back of the truck, which worked great.
Breaking it once it's scored is actually not that hard, though it is dramatic.
However, we discovered one of the pieces wouldn't break along the score line, so, thinking it was just too thick, we got out our tile saw (with the diamond blade) and started cutting it that way, after spending a bunch of time setting up a system to slide the glass across the saw.
Well, turns out that piece was tempured glass... which shatters just when you start cutting it a little bit. what a mess.