It's not an embedded scenario per se, but we use it like we would use sqlite. We install MongoDB as a service with our installer. But it's on the local machine, and only that machine (as our our application runs as the server).

MongoDB isn't as light as sqlite, but for our usage the difference was negligable with MongoDB running with around 3MB memory footprint. In the end we get speed and ease of use/flexibility of not having to deal with sql or schemas.