Hey,
I've made the same thread on plesk forums, asking this question here as well.

I've been pulling my hair out on this one. I install mod_suphp via the rpmforge repo, configured it (used various different guides) but in the end it doesn't work.
I'm expecting suphp to kick in and force the server to throw a 500 INTERNAL SERVER error (like it does on a WHM serve) when i try running a file owned by root and with 777 permissions, but it let's it run.

I printed the user with which apache was used to render the file and that turns out fine, but at the same time i have second server with plesk and no suphp and that does the same thing.

I am not sure about the details of how to resolve this but a good start might be to show output of uname -a

Also include the Operating System name and version if not reported by uname.

+ Version of mod_suphp package

This might help people 'pick apart your issue'.

Hey,
I discovered that the domain was set to use fastcgi, switched to dso and it started to work.