They tend to either bounce, explode or sink into each other.

look at this little newton demo i made: newton_demo1.zip ~4.5mb

i haven't experimented with the newton engine very long but it's amazing how robust the simulation is. no object jitters and even if all objects of the level lie on a pile nothing explodes. the auto rest feature sometimes stops objects too early (i guess this could be optimized a little with some parameter tweaking) and this can look unrealistic. but it's much less distracting than objects which rocket away for no apparent reason. and even if the auto rest feature is disabled nothing tends to explode, the simulation just eats a lot more performance.

...
i like both physics engines, they both have their strengths and weaknesses!