In my opinion jacks stands are used incorrectly. Most people wont spend the time to put the entire car in the air and support the vehicle correctly. This is why you hear of folks having the car fall on them. If the jack stand is not level and not placed on a spot on the vehicle that is both structuraly sound as well as sitting level on the top of the jack stand, then yes it will be prone to tipping over. Wheel chocks will help, but really the entire car should be supported on 4 jack stands. I have (4) 4-ton jack stands that I use for both my STi and my 69 Ford Bronco. I also have a 4-ton hydralic floor jack that gets both my vehicles up in the air as EZ as pie. The few extra seconds it takes to get the opposite end of the vehicle supported is worth it since I know I won't get squished like a bug.