Alas, I will be lucky to get one decent box on which to run our site.  Here at "megacorp" it is a pain -- in time and paperwork -- to request new hardware.  So much so that I chose to drag out my old laptop (900 Mhz AMD Duron/256Meg RAM) to use as our development-server.  In any case, given the small number of users (<1000), I think one production-server will suffice.
In a message dated 10/12/2004 1:44:10 PM Eastern Daylight Time, writes:
I don't reccomend that, esp. if any of the other sites will use MySQL.
Better to have MySQL and other essential services (like sendmail, etc) on
it's own box, and have one box as a webhead. That's basically what we do