Pronamic just launched the first official version of the Pronamic Post Like plugin. With this plugin WordPress developers can setup an like/vote system for WordPress posts. It also has basic support for Gravity Forms to implement a vote/link system via Gravity Forms entry notifications.
You can add a vote/link in a Gravity Forms notifcation by adding the following shortcode:
On the Gravity Forms admin entry page you can check if an post like link in a entry notification was used to like the post.