I'm in the process of developing a method to automate new virtual machines into my environment. 90% of our machines are virtual but the process is similar for both physical and vmware based images. What I do now is I use cobbler to install the base OS. The kickstart script has post hooks to modify the yum repo and installs puppet and func. Once the servers are running, I manually add them into nagios and sign the certificate via the puppetmaster. I've since migrated most of the resources to use mysql as the backend.

I wanted to see what others are doing and my goal for 2011 is to have puppet inventory the hardware into mysql, and somehow i'll script a python script to have nagios grab the info and automatically add it for monitoring purposes. It's kind of tedious to have to add each new server into nagios, puppet's dashboard, munin, etc...