I have to say WOW. I'm very impressed with the Knoppix 6.0.1 install I just did. I'm glad to see they chose to go with a more lightweight approach than other distros.
I have an older laptop that seems to get slower and slower with each update of Ubuntu. I once decided to kick Ubuntu out and install Gentoo on this laptop. It really was faster with Gentoo, but one update kill X and I had a hard time figuring out what killed it. I put Ubuntu back on, but it was so slow that I just ended up not using it anymore. I decided to have some fun and try installing Gentoo again, but the only boot disk I had was this Knoppix disk from a coworker. I noticed that instead of Gnome or KDE, Knoppix chose LXDE for it's default windowing system. Fantastic! I was running this with Gentoo and liked what I saw. I decided to go ahead an install Knoppix to the hard drive to see how it performed.
I've only had it installed for about a half hour now, but it's pretty snappy on my old system and even has some good Compiz effects running. I also like that Iceweasle is the default browser.