Do you have some old Joomla site (pre Joomla 1.5.6)? then is very likely you will got - or already have - a site running only halfway, full of errors saying
Deprecated: Function eregi() is deprecated in somecomponent...
or
Warning: Parameter 3 to showItem() expected to be a reference, value given in /home/someaccount/www/www/joomla/includes/Cache/Lite/Function.php on line 100
Yeah, you might allready guessed it, the PHP 4.* end of life-cycle is wreaking havoc in Joomla 1.0 sites and some early Joomla 1.5 implementations - or even newer sites, having badly coded third party extensions installed.