Top-heavy, but not a preferred or obligatory quadruped like the initial reconstruction suggested. It's a good stance for occasionally using those front limbs to help drag itself out of a muddy shoreline, as suggested by one of Funkei's links a little while ago.
Kind of a shame though, a quadrupedal theropod would have been pretty damn cool.
Interesting to note, Ibrahim/Sereno etc's study states that the sail bones are poorly vascularised, and it seems they don't think it would have been used as a heat regulator.
Not sure I agree with that, the bones' solidity is part of the animal's aquatic adaptations, and we don't know enough (well, anything) about the nature of the soft tissue that surrounded the spines.
