IIRC perl 5.8.0 used to set STDIN & STDOUT to unicode when you had $ENV{LANG} set to a unicode language/encoding (like en_US.UTF-8) but that caused too many problems with backward compatibility, so now you have to explictly set the output and input encoding.
Note that use utf8 only sets the encoding of the script. It has no influence on the input/output encodings.