unrealBook Mobile uses a new type of Dropbox sync. When unrealBook Mobile interfaces with Dropbox, a folder called "unrealBookMobile" is created in a folder called Apps. The Apps folder is created in the root folder of your Dropbox account.
So the hierarchy looks like this:
<dropbox account root>->Apps->unrealBookMobile
You can place files in the unrealBookMobile folder for later access through the Dropbox selection in unrealBook Mobile.