I've been making good progress on getting KDE 4.4 (release candidates) working. It's been quite an interesting ride, in both a good and bad way. =)
First, there's the fun of 10.6 making it even harder to have code that forks without it accidentally exploding on the CoreFoundation fork-without-exec prohibition. I was able to solve this with a combination of fixes from macports' kdelibs4, and some of my own code which changes things to use low-level POSIX APIs instead of Qt APIs for some bounds-checking before execution.
Next, there's the fun of Phonon. KDE 4.4 requires a newer version of Phonon than what ships with Qt (even Qt 4.6). On OSX it gets even hinkier, since the QuickTime plugin for Phonon requires private Qt headers, so the only sane way to build it is to build the Phonon included with Qt, rather than building it as a separate project.
I ended up adapting a patch the Kubuntu folks use to inject a modern Phonon into Qt 4.6. In the process, I finally got around to learning my way around Git (and gitorious), and have set up my own Qt branch which includes my (binary incompatible outside of Fink) patch to Qt to fix plugin-building, Phonon from kdesupport, the kde-qt (formerly qt-copy) changes, and my patches to Qt that splits OSX into two platforms, Q_OS_DARWIN (i.e. use raw UNIX APIs, no Core*), and Q_OS_MAC (standard Qt/Mac).
Long story short, I'm getting there. I've gotten about half of KDE 4.4 RC1 built and apparently running reasonably. RC2 was just released to packagers, and I'm testing out my move to Qt 4.6.1 from 4.6.0, but once I get everything test-built on 10.6, I'll go validate everything on 10.4 and 10.5 (including making some DBus fixes for 10.4).
After that, the next thing to tackle is Mono, and then eventually I'll see if I can get KDE3 building/working on 10.6.