Moving your first line to the bottom does it for me: http://jsfiddle.net/tcloninger/SEmNX/
$(function () {
$('#serMemdd').change(function () {
var k = $(this).val();
if (k == 1) {
$("#serMemtb").attr("placeholder", "Type a name (Lastname, Firstname)").placeholder();
}
else if (k == 2) {
$("#serMemtb").attr("placeholder", "Type an ID").placeholder();
}
else if (k == 3) {
$("#serMemtb").attr("placeholder", "Type a Location").placeholder();
}
});
$('input[placeholder], textarea[placeholder]').placeholder();
});