Ubuntu 9.04 running headless under the basement stairs serves my home network.
Two Compaq Evo T20 thin clients run TC+FLWM with just enough extensions to serve as VNC viewers. The units are diskless; each has a 1GB USB drive plugged in the back permanently to store TCE files. Each drives a 1280x1024 LCD monitor, and the admirable 'synergy' extension lets me use a single keyboard and mouse to
work both at once. These little boxes get the TC kernel and initrd over the network, having only grub loaded into their small internal flash memory.
Across the room is another VNC-based thin client running TC 2.2, but on better hardware (Intel D945GCLF2D board with northbridge fan replaced by passive cooler). That one has the TC kernel and extensions on its internal hard disk drive, all in TCE style so that after boot I can turn the drive off using hdparm and have a silent system.
My Acer Aspire One netbook dual-boots TC 2.2 and Ubuntu 9.04. At home I choose TC because it has scripts that make a wireless connection (VNC again) to the main server completely automatically. On the road I use Ubuntu because it has the full suite of specialized software I need to get work done when there is no more powerful CPU I can access effortlessly. (Also, introducing the little toy to a new wireless network is easier with Ubuntu's GUI tools.)
My office machine is running TC+VNC, too, but it boots from a USB key that I plug in only long enough to boot and then remove. In an earlier TC installation some evildoer installed a rootkit on my machine--which was at that time directly connected to the open internet with no firewall. Yanking the boot device out of the box now gives me
reasonable confidence that my system is hardened against outside interference. Then I leave the machine running continuously between TC version updates (which, so far, has been under a month each time!).
The 915resolution extension is essential for me: I have a couple of widescreen monitors that even work with Xvesa after the right 915resolution commands are given.
To answer the OP's question, the HDD space for operating systems in my machines is about 98% Ubuntu, 2% TC. In my heart, TC gets 60% of the love; Ubuntu gets 40% for respect and vanilla utility.