[Note: this review applies to version 0.3.2. I haven't tested 0.4.0 yet]
Very easy to use. I like how easy it is to backup your site while excluding unwanted directories. It's also great for developers who need to clone a site for testing purposes. Here's a real-world example:
I wanted to try a theme's updated version to see how it would affect my blog's performance and appearance, but didn't want to update my "live" site. I set up a new DB on my host, ran Duplicator, copied the backup .zip and installer to a newly created directory, ran the installer - which prompts you for your DB details, among other things - and the cloned version of my WP site was up and running. A very fast and painless process.