Regarding a few things Boudewijn Rempt wrote about the look of KDE:
1. I actually thought Keramik was stunning during the early builds of KDE 3.1 - it was the perfect balance between good eye candy and not being so noticeable that it got in the way. Unfortunately, I believe it changed in the final KDE 3.1 (please correct me if I'm wrong) and the gradients became too striking.
I liked it in combination with KDE 3.1's bluish icon set, which was sadly replaced in KDE 3.2.
I still use Keramik with the KDE 2 colour scheme and I like it better than Plastik (which is still a very good theme).
2. The window colour changing on focus switches in KDE 4 is a feature of the style, I believe. It is really slow indeed on my old graphics cards as well and for a while I thought it was a palette bug, until I realised that it was supposed to be highlighting the focused window.
I'm sure this will be fixed eventually but I'd still expect KDE 4 to be a tad slower than KDE 3 because of Qt4's automatic double buffering. But I think this is a reasonable price to pay for less flicker.
On a side note, for those of you who are wondering, that automatic double buffering is actually done per top-level window, rather than per widget (I looked inside the Qt code for this and it's actually quite clever).