If you are like me you develop on a local machine and push out your work to gitHub and then the production server. We run Litespeed web server on our data center and so we develop with a local instantiation on our Macs. Mountain Lion, Mac OS 10.8, monkeys around with web components upon installation and while it doesn't destroy your hosts file your local sites running PHP will not load.
In short, If you're running Litespeed, you will need to recompile PHP after installing Mountain Lion, which can be done in about 20 minutes using the Litespeed GUI. You do not need to purchase Mac OS 10.8 Server.