Well, I've been a KDE addict since I first recognized it (that was 2.0, if I remember right), but now it looks like I'll have to look for something else. Why ? Long story short:
I've been following KDE4 development since 4.0, tried every minor version since then, discovered nice new features, learnt to do some things in other ways than used to, so far, BUT: despite all recommendations/tips/tricks/hints (and even slight improvements) it has clearly turned out that KDE4 is a RESSOURCE HOG, turning older computers into slugs, outright horrible responsiveness, whereas the same boxes are snappy as hell when run with KDE3.5. And no, I do not suppose a modern DE to be able to run nicely on 486 PC's with 64 MB RAM :) .
What I'm actually talking about, are my 2 DELL GX 270's, 2.4 Ghz CPU, 1 GB RAM, onboard intel 865 graphics, and a comparable AMD Duron box (SiS graphics onboard). Oh, yes, I know, this is NOT current state-of-the-art hardware, but IMO not too outdated for everyday web-browsing/email/spreadsheet/web development work - KDE 3.5 still proves that very well. KDE4, on the opposite, is just horribly slow: switching Desktops/Applications, e.g., as well as (de-)activating yakuake just leaves the impression, the sytem has first to think about (~ 1 sec. or even more) if it really should do what I want - and this is, what really pisses me off. As already said, none of the tips/tricks/Xorg-configurations or whatever else I tried upon recommendation here or anywhere else, has improved this significantly so far.
So, it seems clear to me, the KDE folks have decided to just follow the M$ standard of doing things: with every new version of the OS/Desktop, users have to buy new hardware in order to be able to work at a reasonable performance. To some extent, I can agree with this, but not in a such obvious and oppressive way.
So, for now, this is the point where I'll cease to follow KDE4 development, as well as installing/trying new versions of it (Last try was Kubuntu Karmic, KDE 4.3, 5 days ago, which promised to solve Intel Graphics drivers issues/performance - outcome: even more horrible than before with Jaunty). I'll just stick with 3.5.10 as long as possible, which ATM serves all my needs (running on Debian Lenny btw.) very well - including Quanta as one of my key applications (still no KDE4 version available, if ever). Although I know, that will come to an end, at least with the end of support for Lenny.
It's a shame that noone in the KDE Community is willing to keep 3.5 alive in a way that it will just run as-is on future Distros (specifically: kernel/glibc/Xorg versions). But if anyone out there steps up doing so: count on me as a volunteer (be warned: my C++ programming skills are still rudimentary :D). @all others: recommendations for alternatives welcome (even GNOME ;-)).