Upgrade to PHP & MySQL 5x?


I am perfectly happy running PHP 4.x and MySQL 4.x. Is there any compelling reason why I should consider upgrading?

Are there issues that would causes headaches IF I did indeed upgrade?
PHP 4 is officially dead and only being updated to address serious outstanding security issues, however if you use a lot of cheap/free code from the internet that uses any of PHP's OOP features, odds are very good that it will no longer run in PHP 5.

Jumping from mySQL 4 to 5 typically involves manually resetting a lot of passwords. If you're not comfortable administering mySQL via command line then it's not something I'd recommend bothering with unless you know that you need some specific new feature of 5.
Thanks for the response. My previous hosting provider had the option of jumping back and forth between PHP4 and PHP5. Is this possible with CPANEL?