I wrote about the performance of KDE 4 some time ago, and I'd like to revisit it. After a few threads about debug builds and release builds on kde-core-devel I figured I was wrong in my previous entry, KDE 4 couldn't easily be build without debugging symbols. So my build WAS a debug build. But now it's possible to have it clean and fast, and I did indeed see an increase in performance when trying it.
Apps start up even faster, it's rather weird to see an application which always took a noticeable delay to start up now pop up like its a basic calculator ;-)