Of course there’s always the entirely DiskLess option, but that requires a DHCP and TFTP server that one can configure. Not always an option.
I’d like to configure a system exactly like the LiveCD + USB PenDrive for persistence, except that instead of a PenDrive (because, e.g., the system only supports USB 1.1) I mount a network filesystem (NFS, Samba, whatever…). The point is that the system boots from CD and not the network, then uses the network for persistent data. For all I know it’s out there, but I haven’t found a way to do it in 5 minutes or less.