Hi,
I've reproduced the crash of the System Preference.
Just after installing Avast! 8.0 you can open Avast! preference and configure the program without any problems.
However, if you will fix the permission of the system disk (I regularly do it), then you can't configure Avast! any more.
It is still possible to open the preference pane of Avast!, but when you click any options, then System Preference will crash.
I installed the very latest version released yesterday (8.0, 40005).
I'm not a programmer, so I don't see which is a cause (Mavericks or Avast!8 ), but there should be a problem.
I just hope this problem will be fixed as soon as possible.
I hope it will help! Thank you!
Edited: removed unnecessary emoticon.