What do you mean ?, isn't Ubuntu or others have Live CDs of their own?
True. But as said before, the hardware detection or configuration in general in those distributions aren't optimized in the live-cd mode that much, thus if you want to use those GNU/Linux distributions as your desktop and integrate/configure your hardware to their fullest extent, then you gotta install them and configure them later rather than once inside their Live CD/DVD versions.
But KNOPPIX comes pre-optimized to work as a completed Live CD desktop and has been around for few years now... thanks to the develper's experience + the pre-installed packages of propriety drivers, multimedia codecs, etc, it's a pretty cool and feels like a "completed" Live desktop environment in my experience.
Anyhow, two days ago they've released a new version of KNOPPIX (6.7.1) below are some of the new features...
*. Starting with the version 6.0 they've decided to ship LXDE (0.5.1-4) as the standard desktop instead of the Qt written KDE in the past. This also makes sense, since LXDE is a lot faster than KDE which should help to speed things up (especially if you use a CD drive where the output MB/S a bit slower when compared with others media).
*. Comes with the LibreOffice 3.4.3 instead of the OpenOffice.
*. Uses the "nouveau" (the reverse engineered version of the proprietary Nvidia driver released under GNU/GPL) including 2D and 3D rendering.
*. Firefox 6.0.2 is the default web browser. But if you happen to download the DVD version, then you'll find Chromium 13 as well.
*. ADRIANE updates: This is the visually impaired optimized package in KNOPPIX and with this released they've done few enhancements + better scanned text recognition and several cell phone models support, etc.
*. GIMP 2.6.10-1.
*. Comes with both MPlayer 2.1.0 rc4 and Gnome Mplayer versions.
*. FFmpeg multimedia library (0.7.1-4) so you'll be able to watch all the proprietary multimedia codecs.
*. Abi word: Only in the DVD.
*. Synaptic 0.70 package manager.
*. eViaCam: Another one available in the DVD which lets you control your mouse using your head motions (via a Webcam) and few other recovery utility, etc.
These are just a handful of updated packages to mention. You can get it from this KNOPPIX download page but if you find those FTP servers to be a bit slow, then as always, I humbly advice you to try this Torrent version (which is fully legal :P) instead. Good luck.