You can retrieve the date by using the getDate function:
$("#datepicker").datepicker( 'getDate' );
The value is returned as a JavaScript Date object.
If you want to use this value when the user selects a date, you can use the onSelect event:
$("#datepicker").datepicker({
onSelect: function(dateText, inst) {
var dateAsString = dateText; //the first parameter of this function
var dateAsObject = $(this).datepicker( 'getDate' ); //the getDate method
}
});
The first parameter is in this case the selected Date as String. Use parseDate to convert it to a JS Date Object.
See http://docs.jquery.com/UI/Datepicker for the full jQuery UI DatePicker reference.