I used to use IO::File for the cleanliness back when "open my $fh" didn't work. Or when I didn't feel like the overhead sometimes I used gensym (remember that?). I'm aware of all those advantages and mentioned most of them in the original post; and I still like the idea of automatic close :)

Can you explain why explicitly closing output filehandles is especially important? Modulo close failures, in our case the close *will* happen, together with associated flushing.