I installed Kubuntu
on my Thinkpad 600E yesterday, and I've been gradually been tweaking it so I can live with it for the rest of the month. The laptop (keversei) has had Gentoo on it for a number of years. It was as fast as you'll get a modern OS on a 300MHz Pentium 2, but it was literally spending days
On the topic of switching away from beloved but unsuitable software, this is the first time I've used KDE since version one point something. I tried regular Ubuntu, but GNOME was unbearable... headdeskingly slow. Firefox on linux has always been pathetically slow, but this was heartbreaking. Konqueror on KDE is somewhat better: rendering times are about the same, but scrolling is much smoother and the GUI is more responsive.
I had to compile MPlayer and Xvid myself, even though I asked for non-free software? I remember there being an MPlayer package on regular Ubuntu, so maybe I'm doing something wrong. Trying to figure out what all the -dev packages, autotools, and other compiling prerequisites were called was annoying. Not installing sshd by default is unjustifiable.
I'm warm to KDE, though. It looks good, it's customizable enough, and most importantly it bogs down less than GNOME on slow machines. I can set up most things with the GUI (KPPP is just not capable enough for GPRS over bluetooth). The biggest problem I see is that there's no wireless network applet to tell me my signal strength and available access points. Finding APs is pretty important, and I'm not sure how to do that without dropping to a console.
Don't worry, I'm still running Gentoo and e17 on atlas :)