Here is the solution, via the YUI forums. This might help someone in the future:
YUI().use('node', function (Y) {
var re = / {1,}/g;
var div = Y.all('div[class *= " "]').each(function (n) {
var numClasses = Y.Lang.trim(n.get("className")).split(re).length;
n.addClass("numClasses" + numClasses);
n.setContent(n.getContent() + " found " + numClasses);
});
});