I'm actually in the process of writing a short guide on the subject of integrating ContentTools into your CMS because this question has come up a number of times since the library was released last week.

We currently use the library on a number of client sites (including the getcontenttools website which promotes the library itself). The role the editor plays is determined by the balance of content. On the getcontenttools website new pages are added by creating a new template file in a relevant directory (e.g /tutorials/adding-content-tools-to-your-cms.html) at which point I can navigate to the page and use the editor to populate it with content (IMO it's preferable to writing markup or HTML) - so in this instance ContentTools is pretty much the entire CMS interface (there's a fairly detailed description of how this is done in the Saving strategies tutorial).

However clearly in many cases content is better edited through traditional forms (no one wants to try to build/parse a product discount matrix written using a WYSIWYG editor). So typically in these scenarios ContentTools is used to enhance the functionality of an existing CMS not replace it. For example on an eCommerce site users might add a blog/page/product using a traditional form but when they wish to edit the item's content the CMS would switch to a front-end preview of the item and allow the user only to update the relevant content (e.g the content of a blog article or page, the description for a product).

ContentTools does not attempt to replace the CRUD facilities of a CMS (it's beyond the libraries scope) but rather to provide users with a more natural editing environment.

Hopefully that helps answer your question, if you keep an eye out next week for the tutorial on integrating the library into a CMS I'm hoping top provide some screencasts showing how we've achieved this on different sites.