Another thing is I understand that overriding magic methods like __toString is not a good idea and right way but PHP has some openness which has allowed us as programmers go the non-standard way and it's now good that going ahead we are stopping some of this bad practices by letting this go.

@Jonathan thanks for updates.

For starters it is not true that "magic methods" do not accept arguments , it is merely the _toString() magic method which I do not see having a real need for arguments , should you choose to pass an argument to symbolize a certain format the _toString() should operate on you can set that prior to calling the function with a class variable.

I believe that upgrading to 5.3 is mainly important when developing new applications since you would mainly use new features suggested like advanced OOP techniques and name spacing , should you choose to upgrade your application from 5.2.9 to 5.3 consider upgrading your code to use more advanced techniques and not just standing in compliance with the new 5.3 changes , though I admit that 5.3 brings many changes that break existing code in most cases I still see it as a vital stage in application development , PHP is taking a new direction and it would be wise to follow it

Most problems could be solved by going through:
http://www.php.net/manual/de/migration53.php

alas regarding external extensions like that one for PDF I have nothing to offer.

Put in the extra effort , it is important to stay with the curve and utilize as much as you can from what 5.3 has to offer!

As for the datetime problem, that can be solved by setting the datetime.timezone setting.

Overriding magic methods with parameters is also not a good idea, you aren't using them properly if you think you should add parameters. As for your your example, you should have used a toString function which calls __toString if having default arguments.

However, yes, other than that there is one issue I've found with upgrading to php 5.3. the use of references and call_user_func*. This is a big problem in some Drupal 6 modules, which use references a lot in its hooks. They are trying to keep it working for the very outdated PHP 4 still as well.