Some common changes that you must make when moving from non-secure php environment to suPHP:
For example, if your site had these settings in a .htaccess file:
php_value post_max_size 10M
php_value max_execution_time 30
SuExec users must put them in a php.ini file instead. Here is the proper syntax:
post_max_size = 10M
max_execution_time = 30