I was also skeptical regarding the readability of prefix notation vs. postfix for large problems. However, when I tried it, I actually found it easier to handle. For example, here's a very obnoxious heat transfer correlation that I typed in common lisp:
Now, I admit that my sense of whitespace is pretty inconsistent, but still: Here is a real case of a very annoyingly nested expression in both infix and prefix notation. While I think it would take quite a while for anyone to sort out what the Hell is going on for either of these regardless of experience (versus, say, rendered LaTeX), I would put forth the suggestion that the common lisp is actually easier to understand.