Not sure it's still important after 3.0 release. Confirmed in trunk:

import codecs

class X:
  def __unicode__(self):
    print 'unicode'
    return u'unicode'
  def __str__(self):
    print 'str'
    return 'str'

x=X()
f = codecs.getwriter('utf8')(open("/tmp/out","w"))

print >> f, x # 'str'