Secure shared hosting environment basics

[Simon]

Hi There,

I know this question has probably been churned over and over in various different variations, so i applogise in advance if its one of those 'here we go again…' posts :)

We are a hosting provider that is currently using the LAMP stack to host our clients websites. 80% of these are on our shared hosting instance that currently has PHP 5.3 using safemode to assist in keeping sites to their own area. We are looking to build a new shared service and have been playing with nginx/php-fpm (on debian squeeze) and love the easy configuration and speed.

My question is: What is the best way to go about setting up a shared hosting environment for 1000's of customers, which is secure from the point of view that the customers can't access other sites. 

Im not looking for a how-to, really just a "this is the correct way you should look todo this" hint that will point us in the right direction….

Thank you for reading!

PS: Would like to stick with debian if thats possible

Simon