An upgrade to a language should not make such sweeping changes that experienced programmers must relearn vast amounts of material.
If my above quote didn't work, ahh well 😛
developers that are comfortable with 4 are fine with the move. 5 basically moves more into OOP where 4 has the features, just more difficult.
All I am saying is that learning PHP 4 OOP is not the easiest (for me anyway). 5 is easier with built in functionality like passing the object between functions. In 4 you had to pass the entire object, where in 5, its automatically remembered.
If you really want to view a list of changes, check www.php.net
Ta.