found a bug description which describes my problem exactly:
https://bugs.kde.org/show_bug.cgi?id=261180

Frequent problems with dbus-daemon entering a runaway state, consuming 100% of
one core for extended durations. KDE applications fail to open or react in a
timely manner while this is happening. Screensaver never happens.

Steps to Reproduce:

Haven't been able to identify a particular usage pattern. Typically takes several
days to a week to reoccur. Always happens eventually if I stay logged-in for significant periods of time.

Seems linked to login duration. Running KDE apps (or dbus enabled apps)
include: the KDE desktop, Krusader, Konsole. Common non-KDE apps include: Firefox, Chrome, Eclipse, VirtualBox(non-OSE), Pidgin, Skype, Dropbox, System Monitor.

Actual Results:  
One core at sustained 100% cpu. Launcher won't start new applications, usually have to reboot from command line.
Restarting the daemon doesn't seem to have an effect.
While killing it makes the system unusable irrespective of a future daemon restart.

Expected Results:
dbus shouldn't hog CPU
restart dbus should return the KDE env to a viable state after killing the process


Additional Information:
KDE 4.5.1 on Ubuntu
8 GB or RAM (probably unusual)