While there is no option to work on a single document at the same time, like you can with Google Docs and Zoho Writer, it features all the things you'd want for putting together a sturdy document. You can pick from various fonts, format to your heart's content, and drop in photos--either from your hard drive or a URL. All the while it saves what you're doing and even lets you roll back to an earlier version if someone has gone in and botched something. You cannot, however, see what was added or replaced without first opening up the file.
Permissions have also been handled with some convenience in mind, although there are definitely some rough edges. If you start a document in a folder you're already sharing with other people they are automatically chosen as collaborators. You can then go in and choose whether you want them to be able to edit the document, or simply view it.
Oddly enough though, you can't send collaboration invites from a virgin document; something I'm assuming will be fixed in short order. In the meantime you need to do this from the folder where the document resides. Here you're given the option to send an invite either as a viewer, or an editor.
If you're sending the document to someone who is not a registered Box.net user, they'll need to sign up for the service to edit it. This is where I found it to be a little buggy, since the service doesn't even give them an option to skip registration and begin editing as a registered guest, or simply see a read-only version of the document. In its current iteration they either need to sign-up, or get you to re-send the invite to view only before they can even lay eyes on it.
Despite this niggle, this feature is off to a good start, and a smart way to extendI would have been happier to see it replaced with third-party services that let you do the same thing , but in this case, these documents can be a great natural extension for the service's built-in discussion tools.