The "disabled" attribute for form fields is a great little user interface helper that you can use to help protect data from accidental changes. It locks down an HTML input form element so that it can be viewed, but not be changed. This is handy when displaying a form to a user where you need an extra layer of protection for the data.
What happens when the user goes to submit a form with disabled elements? The value of the disabled elements are not passed back to the browser - this can quickly turn into a data validation and/or submission issue.