[*]Install directly from the Internet from a business card sized CD:
http://www.debian.org/CD/netinst/ .
[*]Use redundant levels of software RAID, even Vista Ultimate only does span and RAID0 AFAIK
[*]Not lock you into one vendor, if you don't like what Novell's doing use RH/FC, if you don't like what RH/FC's doing use Ubuntu, etc.
[*]Let you talk directly to the developers of the software you're using for free and even participate in the development if you'd like.
[*]Run single apps seamlessly across the network. I know Citrix can do this and I think TS can now, but I'm not sure about the licensing.
[*]Use all 4G of your memory with a 32-bit kernel. Although it's probably a better idea to just run a 64-bit kernel even if you want a 32-bit userland.
[*]Use a 100% 32-bit userland with a 64-bit kernel.
[*]Compress and encrypt your memory image when you hibernate. Not only does compressing the image save you disk space it makes suspending/resuming faster since there's less I/O.
[*]Run with a root filesystem mounted via the network.
[*]Update all of the installed software from a single source. Of course, once you go outside of the distro's repository this might not stay true.
[*]Set a block device read-only so that you can do forensics and be 100% sure that no writes will happen to the device.
[*]Setup Mandatory Access Controls via SELinux to enforce extreme levels of security.
I'm sure I could come up with more given enough time.