Migrating from PHP 5.1.x to 5.2.x
Notable changes include:
- __toString() being called in more circumstances than before
- abstract static methods raise E_STRICTs (since both abstract and static doesn't make OOP sense)
- Date/time functions may issue warnings if you haven't set the default timezone
5.2 also includes a large number of new or expanded functions, methods, classes, constants, and other stuff.
On the bright side the changelog isn't nearly as complicated as it is upgrading to 5.3 or 5.4
In my mind there's 5.x, 5.3, and 5.4.