Well, a basic content editable block does nothing but trigger focus and blur events and allow the user to type in and change a block of content; but you will need to write any code, much like an input, to make the block interactive. This code will probably need to update your database, provide feedback to the user in case there is an error, allow the canceling of the change, etc.
It might even be a good idea to add some basic editing controls (if you want to make it into a WYSIWYG editor) like bold, italics, indent, etc.
If you can do all of that on your own, then sure don’t bother with any plugins. Otherwise, I would recommend checking out something like [Aloha Editor](http://www.aloha-editor.org/).
