The poo can have quite the robust aroma, but this usually isn't a problem if you a)clean out your Viv regularly and b)use a nice absorbant substrate, something like aspen bedding.
As far as the size of it, that depends totally on what your snake is eating. Obviously, a pinky makes a much smaller turd than an adult mouse will. Anyway, it hardens pretty quick, and is a sinch to scoop out of there.
Just don't be freaked out if when your snake feeds on larger prey, the poo has a nice soft fur coat. (Fur is, for the most part indegestible).
Jason