I'm always a fan of not using a plugin unless I have to. Here's a few tips to do it yourself. As mentioned above, the following added to your wp-config.php would limit revisions to a maximum of 2 for a post (older ones get overwritten by the newer ones):

define('WP_POST_REVISIONS', 2);

The following line would limit revisions to be saved once every two minutes (120 seconds) when added to the wp-config.php file:

define('AUTOSAVE_INTERVAL', 120);

To delete all revisions from your blog, execute the following SQL query from your phpMyAdmin:

DELETE FROM wp_posts WHERE post_type = “revision”;

Hope this helps someone.