The computer with the TV encoder in it is booting completely over the network (using NFS root).
Also if getting a single system MythTV system setup had problems getting it to run over the network was even more "fun". It took me a while to figure out how to configure the secondary (slave) backend. One of the important details is that when you clone using debootstrap, you really need to change the name of the new system for mythtv. If multiple systems in a mythtv network have the same name, they'll try looking for encoder cards that are over in the other system--this makes the mythtv backend die, and is frowned upon.
Once I figured that out, I then learned that they really mean it when you need to go through and just run the mythtv-setup program on the client. You need to do it (which when the client is going to be a headless box in a corner means either setting X up on it, or running mythtv-setup over an ssh tunnel.
Still to do, I need to figure out why the client isn't automatically mounting the nfs filesystems. (needed for myth since it needs to find the database connection file). It'd also be nice to set up kerberos and/or LDAP so I can cut down on the systems and passwords I need to remember. (Not to mention NFS4 looks to be more secure than NFS4)