Yes, you could do that. Won't judge that approach - that's probably a cultural thing. But you have access to side effects and could dump stuff to the console (even, if you're so inclined, using the .Net framework standard way, calling Console.Write/WriteLine - although the print* stuff in F# is really better suited if you decided to go down that path).

Yes, printf is easy in F#. The following example works in F# and OCaml:

  let rec fact n =
     Printf.printf "%i\n" n;
     if n = 0 then 1 else n * (fact (n-1))

For the record, this was sarcasm. It's 2012. I really hope you guys aren't debugging using printf still.

You'd think someone into esoteric languages would've heard of a debugger.

OCaml, on which if I understand it correctly, F# is based, allows you to do that easily, but it's not really natural to do so in this programming languages.