does jacking a car damage the subframe bushings?

[erubin]

When i jack a car on the frame I notice that the subframe bushing gets stressed/seperated. Can this damage the subframe bushing?

On a separate note, I sometimes only use a floor jack to raise and hold a vehicle's corner up. The jack stands come out if I'm going under the car. My question is, do floor jacks ever fail and drop a car catastrophically from a hydraulic seal failure? My floor jack is a 2 ton Harbor Freight one that is 25 years old.