I only don't like that I have to manually call validate for one Checked-Validator on form submission.
Then make changes as noted in the CHANGES REQUIRED section below.
For example, if a user tries to submit a form, but makes no selections, Spry applies a class to the widget that causes it to display the error message, “Please make a selection.” The rules that control the style and display states of error messages reside in the Spry Validation file that accompanies the widget.
The default HTML code for the Validation Checkbox widget, usually inside a form, is made up of a container span tag that surrounds the input type="checkbox" tag of the checkbox.
Either you checked an Interest and it is a Yes/TRUE/1 or you didn't check it and it is a No/FALSE/0/NULL.
Anything else is bogus, and I don't feel compelled in that case to help you out, because you are likely a hacker!! It gives you a unique value you can compare to on POST. It gives you a unique value you can compare to on POST.