We power our linux workstations, notebooks and servers (a total of 130 at the moment, growing fast) with a self-made autoinstallation of Debian (just converting to woody, we plan to publish it when it is ready). Our conf-update package handles the initial installation and hardware detection and configuration as well as upgrades, all non-interactive. Several servers (e.g. mail, a compute server) are also handled this way.
We chose Debian years ago, because we have the full possibility to change everything to our needs and because it is relatively easy to do upgrades (security,...). The well tested state of each release gives us a reassuring stable base to build our additions and upgrades (e.g for new hardware) on.