I'm currently installing SimplyMEPIS on my old machine. And using it to blog at the same time, which I think is quite a neat trick! SimplyMEPIS's install disk functions as a LiveCD first of all, which boots into a full KDE session without touching the hard disk, and installation is then done by a program that runs within KDE. Since when should installing an OS force you to stop using the computer? I like it!
One down side is that the install is probably a bit slower than it would have been otherwise, but for many people, who will want to demo Linux out first, it's ideal.
Installation has now finished, so I'm going to have to reboot soon. If they could eliminate that step, I'd be even more impressed! Some more things while I'm here: it also sets up root password and default login (before you reboot), and allows for installing of vendor graphics drivers (nVidia and fglrx) — I don't happen to need them, but it's a very nice improvement to the hassles that I believe some people with nVidia — it just works out of the box.
Only one criticism so far: the installer asks you to choose your locale, without help on doing so — in my case I chose en_GB.UTF-8, but I only knew to do so because of past experience.