I had some trouble reading nested IF functions, so I wrote a piece of code which translates them into flowcharts: http://excel2flow.asp2.cz/ (weekend project)
It briefly bugged out (dumping everything as a string into a single result block) on entering a ":" or ";" after the word "Error" in a string as part of the long formula I tested it with, but since then I've changed a few minor things and it's stopped happening :S
Thanks for testing! ";" is delimiter for function arguments in czech version of Excel (because "," is decimal delimiter). Parser tries to guess if you're using czech or english version and it probably guessed wrong.
Anyway, I wrote the parser by hand so I cannot guarantee it will work on every valid Excel formula. But I'm working on improved version which will use formal grammar.
It briefly bugged out (dumping everything as a string into a single result block) on entering a ":" or ";" after the word "Error" in a string as part of the long formula I tested it with, but since then I've changed a few minor things and it's stopped happening :S