Having come to Mathematica as a former Mathcad user, I think I understand where youre coming from. One thing you could try as a means of filling up your white screen/paper space is to place your input cells into a grid (which you can create by typing ctrl-comma and ctrl-spacebar to generate additional columns and rows, although to add formatting options (like align left) you will have to evaluate an expression that invokes the Grid function with a placeholder and whatever formatting options you want (I have a basic function that I call to do this and then, once my input grid is formed, I delete the function call - this could be cleaned up by placing the function into a palette). Again, once the grid is formed you can add rows/columns in the same way as described above. Remember to place a semicolon to the right of the grid if you dont want the evaluations to be displayed. The semicolon can be hidden, if you want, by making its font colour the same as the background colour. And its also a good way of mixing text with expressions and graphics in different grid cells.
Another frustration I found with Mathematica is that it doesnt have a built-in means of displaying the result of an evaluation inline with the input expression (i.e. you cant display lhs=rhs on the same line, where rhs is the result of evaluating lhs). This functionality can, however, be provided using a fairly simple function and is another good way of reducing the acres of white space that can result as a consequence of Mathematicas line-by-line approach. As a user of Mathcad and Maple, this is one of those basic options that I miss in Mathematica.
Apart from these and a few other, generally minor, frustrations, you should find that Mathematica makes Mathcad look like a kindergarten toy. Although it does take some time and patience to get to grips with.
Hope this helps, Ian
