Try this as the data is not text child of node, but rather an attribute. Also have a look at the examples in the ECMA357 PDF which you can find from google (E4X).
CF.widget("_PS_DEBUG_").label = [email protected];
I think that _PS_DEBUG_ widget is reserved name and if widget is present on the page, any output you send using system.print() calls will overwrite the label.
Might I suggest using something like (note use of GUI.widget and CF.widget - there is a thread I authored here that discusses the differences. I suggest you use GUI.widget whenever possible except when you must fetch resources from other pages.)
GUI.widget("MY_TEST_VALUE").label = [email protected];