If you think you know what's going on behind the scenes when you're working with objects in PHP5 - you're wrong. You're even being lied to, according to Sara Golemon's latest entry:

If you're among the crowd who have migrated an OOP based application from PHP4 to PHP5, then I'm sure you've heard the expression "Objects are copied by reference by default in PHP5". Whoever told you that, was lying.

As she explains, the truth is more that they behave that way, not that they are actually like that. She talks about what objects actually are and how things are handled differently from PHP4 to PHP5. She also "lies" a little also about the "copying" part, and explains the internal structure of a variable to show why.

She also includes a bit on why referencing variables when it's not really a must is a bad idea - the main idea of it being a waste of space and memory in the application.