PHP Warning: strtotime(): It is not safe to rely on the system's timezone settings.

Questo errore nei log di Apache:

FastCGI: server "/var/www/clients/client3/web4/cgi-bin/php5-fcgi-*-80-example.com" stderr: PHP message: PHP Warning:  strtotime(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier.

e' caratteristico di PHP 5.3 (pare sia sparito con la release 5.4).
Per risolverlo bisogna aggiungere al php.ini la riga:

date.timezone = "Europe/Rome"

personalizzando se occorre la timezone tra doppi apici