That being said, I think there needs to be a more interactive method where you can see things on the stack in real time as you are programming.
I found myself not being able to focus on the problem I wanted to solve and instead was spending too much of my brainpower on remembering what was on the stack where.
If you study human computer interaction and cognetics the human brain can only remember so many short term memory "variables" at once. Programming in Factor uses up too many of those spaces.
I think the problem can be solved though if the development environment shows the stack at each point in time; that way the computer does the thinking instead of the programmer.
One way to do this is to supply some arguments to the word (function) and as you manipulate it in real time you can see how it is transformed. Your steps get recorded as the word.
This solves the problem of programming blind and having to play interpreter in your head as you are programming. Thus, freeing up cognitive space and making the programmer more efficient.