$('#checkbox1').prop('checked')- in jQuery 1.6+, usually the way to go$('#checkbox1').is(':checked')- all jQuery versions, but slower$('#checkbox1').attr('checked')- NOT in jQuery 1.6 - but in 1.6.1 and <=1.5, don't use it
$('#checkbox1').prop('checked') - in jQuery 1.6+, usually the way to go$('#checkbox1').is(':checked') - all jQuery versions, but slower$('#checkbox1').attr('checked') - NOT in jQuery 1.6 - but in 1.6.1 and <=1.5, don't use it