public/private class methods/variables

Hi all- I saw a feature request a few days ago (on bugs.php.net) for the ability to define public and private class methods and variables. I know in our application (www.intacct.com) we would have a real use for such an ability. I'm willing to take on the task, unless someone else is already working on it. I'm basically looking for other peoples' opinions .. would such a feature be useful in PHP? Are there any reasons not to do it? Thanks John