QUESTION:
Can we be sure that a bouncing lander will not fall into a crevace or get
lodged somewhere useless?  Do we know the surface that well? What is
stopping the lander from "landing" on a large rock, and making it impossible
to open up the craft to do its thing on Mars?

ANSWER from Cheick Diarra on November 27, 1996:
The landing is done with the lander surrounded by 5m diameter air bags. 
When the system comes to rest, it is anticipated that the air bags would
provide us with the necessary clearing. They will be then deflated and the
petals, smaller than the air bags would be deployed in the space
previously occupied by the bags. 

The landing site was selected taking into account the particular
concern about rough landing sites. From the Viking images of the Martian 
surface our resolution is generally poor: about 250 meters per pixel.

ANSWER from David Dubov:
We all wondered about this at the beginning. So we tried it! First of all,
it turns out that we had a hard time getting the inflated, 17 ft beachball
of a lander close to a big rock! As long as those airbags stayed inflated,
it wanted to roll away from anything big and pointy. Secondly, even when we
did manage to coax it right next to a wicked boulder, the petals opened
right up even if it meant having the whole lander do a backflip! It took
some work, but we actually made that happen once in our Mars Yard at JPL and
without damage! It really helped that the petal actuators (a motor and a
gear train mounted on each of the three petal hinge lines) had the torque
margin to actually LIFT the lander off of the ground (they can even
indefinitely support the lander in a sort of "iron cross" once open). And
these tests were done under Earth's gravity, which gave the rocks a distinct
advantage. With many many tests behind us, in not one case would it have got
stuck.