jQuery: enable submit when min 1 checkbox is checked

EDIT (11-01-2021) - As pointed out by @Janus Bahs Jacquet, as of jQuery 1.6.1, properties of elements should be manipulated using the .prop() method instead of .attr() method.

$('.check').change(function() {
    if ($('.check:checked').length) {
        $('#sub').removeAttr('disabled');
    } else {
        $('#sub').props('disabled', true);
    }
});

Updated demo : http://jsfiddle.net/kjb0fyr8/

---

You just need to check the length property of the checked array

$('.check').change(function() {
    if ($('.check:checked').length) {
        $('#sub').removeAttr('disabled');
    } else {
        $('#sub').attr('disabled', 'disabled');
    }
});

Here's the demo : http://jsfiddle.net/LUnN5/

Get a reference to all the checkboxes in question, and then on change() event, set the disabled property based on if any of the checkboxes are checked or not.

var checks = $(':checkbox.check');
checks.change(function() {
    $('#bla').attr('disabled', ! checks.filter(':checked').length);
});

jsFiddle.