attr_accessor :return_code

  This should be attr_reader?  It is "the return code from the last
  operation".  Does it make sense to set this?


Binary mode is true by default

  I thought servers set the default.  Is this true, and does ftp.rb
  somehow honour this?


Methods can be made private

  set_socket, sendcmd and voidcmd are not documented in pickaxe or
  nutshell.  Can they be made private so they don't appear in RDoc?


Gavin