I've heard that it is recommended to replace at least one 3 1/2" screw at each hinge into the framing on the hinge side. I figured that two per hinge would work better! I added some 1 1/2 screws into the door as well (replace those 3/4" ones).

Most of the doors used in homes today are not very strong. There are some exceptions but you would generally have to either put those in yourself or spec them during construction if you use a contractor. Most of the "cookie cutter" homes won't have that good a quality door. Some commercial doors with steel frames would be good but probably difficult to get installed.

There are some great videos on the web that show you how to enter a building (firefighter forced entrance), that sort of make you wonder if it is possible to make your house really secure? Guess the plan is to make it harder for the lazy criminals so they leave your house and go next door!