We'll I guess "can't" answers half my question.
The other question is, how do I protect my files? Perms 644/755 won't save me from a vulnerability in a php script anymore.
Worse still, not even 660 perms on my mail folders will prevent an incorrectly written php script possibly sending my mail folders over HTTP.
In the pre-phpsuexec days, at least I knew that 660 perms on my mail folders meant that php scripts can't read my mail folders, unless of course a sysadmin erroneously put apache into the "mail" group.
Am I the only one concerned about this?