haha 'Expression Stacker' was just a name for it because I imagined people dragging and dropping expression bits and pieces onto each other like a stack...or a pile...
Anyway I dont think it's really something that would be useful. Its good practise to learn how to type expressions. I added syntax highlighting and bracket matching to the expression editor anyways.
Here was a final design I came up with
<img src="http://dl.dropbox.com/u/939828/stack3.PNG">
Basically, a 'block' could be setup so the text was in the middle...so the Multiply looks like a proper multiply...and secondly the parameters dont have text for them (Multiply doesn't need text with A, B) then the stack above is lowered.
The only remaining problem with the stack is if you do something like:
5 + 3*3 + 2 you end up with 3*3 as one stack, and 5 + (3*3) as the stack below, then (5+(3*3))+2 as the stack below that.