If you’re looking at the new facebook commenting layout you may be missing something. The “Send” or “Comment” button (whatever is was called) is not there anymore.
When you were writing comments before the recent changes (March of 2011) you could hit the “Enter” or “Return” button within a comment to create a carriage return (create a new paragraph). Now, hitting “Enter” or “Return” on the keyboard will actually submit your comment. Unless you know the secret!
To create a new paragraph in a Facebook comment, you have to click SHIFT+RETURN/ENTER. This creates a new line rather than submitting your comment. Viola!!