After spending some time on implementing a DBUS proxy object, i.e the service object's peer on the client side, I finally found the 100% CPU usage problem I mentioned in my last blog

The QSocketNotifier instance for writing operations is enabled by default, but the DBusWatch it is handling isn't!
"...Note that when a watch is added, it may not be enabled...."
Pah!

So a simple query for the watch's state and matching setEnabled() call on the notifier later the problem was gone and I have an almost complete Qt3 backport of Harald's Qt4 based classes.

The only thing not working that I am currently aware of is an async reply call directly followed by sync reply call.
Somehow the async reply isn't either received or not processed.