[jQuery] Fading out the CONTENTS of a form field (ie: the value)

[RyanJW]

Hiya guys,

I've put together a basic handler for clicking on a field. It simply
empties the field for you when selected, and if you don't enter
anything it puts the default text back in:

$("#field_154038").focus(function () {
        if ( $(this).val() == "Please enter your postcode" ) {
                $(this).val("");
        }
});
$("#field_154038").blur(function () {
        if ( $(this).val() == "" ) {
                $(this).val("Please enter your postcode");
        }
});

This works fine, but an additional nicety I tried to add was a fade in/
out. I've given it a stab but have been unable to work out how to
simply grab hold of the text contents of the field so it can be
manipulated.

If this is possible, could you please tell me how? :)