This is a service that, after you fill in your basic server details, will back up your weblog on a daily basis. It’s currently free so worth using, going from the blurb on the site I think they will start charging and as soon as they do that I’m leaving.
So why use this instead of the built in backup functions of WordPress. Easy answer, the built in backups don’t work. Its function requires access on your host server that many people don’t have, me for example, so the only backups are have are sporodic manual ones. Not really good enough.
A good service? Yep. Worth paying for? Nope. Use it while it’s free.