Conway doesn't specifically mention this, but I find it annoying when there are multiple packages in the same file. When searching for methods or keywords in your editor, it makes it hard to find the right chunk of code, especially if each package is a subclass of the same base.
Jeffrey Ryan Thalhammer <email@example.com>
Copyright (c) 2005-2007 Jeffrey Ryan Thalhammer. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license can be found in the LICENSE file included with this module.