I am having the same issue.
I am running joomla 1.5.25 with php 5.3 and I am getting the following errors
Warning: strtotime() [function.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. We selected 'UTC' for 'GMT/0.0/no DST' instead in /home/www/mysite/libraries/joomla/utilities/date.php on line 56
Warning: date() [function.date]: 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. We selected 'UTC' for 'GMT/0.0/no DST' instead in /home/www/mysite/libraries/joomla/utilities/date.php on line 198
Warning: date() [function.date]: 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. We selected 'UTC' for 'GMT/0.0/no DST' instead in /home/www/mysite/libraries/joomla/utilities/date.php on line 198
I turned off error reporting in Joomla and went into PHP.ini file and changed error reporting to off there as well as added the line to htacccess but still getting the errors.
If I were to set the time zone as it is commented out in the PHP.ini file - what zone do I use. Mine in Atlantic Canada or the California time zone where the server is.. And where do I find out what they are equal to... would Atlantic time Canada be Atlantic or -4 for example.
in advance thank you for your help

Gary