Nate; you've got a gold mine here that answers a question I've been asking for about a week now. I think you could explode this plugin usage on this one attribute:
showing people how to change cookie expiration.
...or creating a field to do so.
i changed your default to be 3 hours for my tastes; because I don't people to leave the site available on a public computer or one that is not there's.
many people do not like the default 10 day expiration and want to edit it. i haven't found a succinct answer, but your plugin allowed me to by adapting code.