When KDE4 was first released I was shocked at the lack of conguration options themewise compared to 3.5 and its wealth of options, I had best note plasma however is a notable exception, a triumph of customisation and SVG goodness!
Kwin has needed a decent engine for theming for a while, while its almost on par in terms of effects with compiz, it has always lacked the extensive customisation features provided by emerald and its various engines.
Then there is the default QT theme in KDE4.3 (oxygen). This has many fans and it is nice to see some technoloigical progress being made in terms of themeing. Personally im not a fan of the whole oxygen look as it wastes to many pixels and is mostly plain grey. In my opinion its only used by alot of people as they lack an alternative.
Currently I’m working on improving KDE4.3 experience in Sabayon, we have always shipped the excellent QtCurve Qt widgetset as a alternative to Oxygen as it very flexable, fast and can be made to look as you like, it also integrates perfectly with a GTK theme provided (no winNT style firefox!).
We have, for all the KDE4 releases, shipped with the default Kwin theme due to the lack of a suitable replacement. Yesterday however, while browsing through KDE-look.org looking for a new wallpaper for my machine, I noted the Aurorae Theme Engine. This engine is designed to KDE4.3+ and uses SVGs to decorate the windows. “Yay!” was my inital thought and I immedietly installed it from the provided ebuild ( a bumped version with some cleanup is on the sabayon overlay now).
Work is now in progress on a theme for 5.0 for keep an eye out for 50._beta3 artwork.