Home depot in Ontario Canada will do 3 straight cuts with a panel saw or radial arm saw. More than 3 cuts will cost you. Straight cuts only, and like others said above, I just have them break the panels down so I can get them in my vehicle. I make sure that the cut I tell them to make is at least 1" off of the actual cut I'm going to make. It helps if you draw a little layout of a 4'-0" x 8"-0" sheet, or whatever you're getting cut and mark the home depot cut line on it and draw down some dimensions to locate it. Hand the drawing to the saw operator.
Incidentally, they are supposed to have only the employees who have taken a safety course operate the saws. On a Saturday, you could wait an hour or more just for cuts. Seems that at our home depot the saw guy is also the fork truck guy, so when he's taking stock down off the racks with the fork truck, nobody is getting material cut.