... and that it is only by browser cookies. The documentation ought to explain that a browser with cookies disabled can vote ad infinitum.
2. Please add a display_comment_karma() function and a display_post_karma() function somewhere in the plugin so the blog admin doesn't need to paste so much code to her theme. By the way, function_exists() is faster and better than querying the list of active plugins, i.e., if (function_exists('display_post_karma')) display_post_karma();.
3. Height and width attributes greatly help recent browsers render images quickly. The plugin's img tags don't have them.
4. createTable() may conflict with other plugins; please rename it.
5. Version 0.11 references a /plugins/SimpleKarma/public.css that doesn't exist.
6. You might be able to save some WP memory by calling some require_once()s only when is_admin() is true.
7. Check out register_script() for the javascript file, and the delete_post action and the delete_comment action for avoiding orphans.
8. An "uninstall" feature would be cool, too.
http://wordpress.org/extend/plugins/simplekarma-content-ratings/