Brother my point of view is that, average interview takes 20 minutes. out of that 10 minuts are consumed by introduction, academic background, family background, daily activities, hobbies, past employment, etc.in short they will ask every thing related to your person WHICH HAS NOTHING TO DO WITH KNOWLEDGE.
then 5 minutes are spent by questions like why you want to join the civil services?why you have opted for that that or that particular group?what are the characteristics of civil servants?etc
As a result we have only five minuts left in which this so-called knowledge is tested.But REMEMBER, during this time, they will ask you questions about the issues that you have mentioned as the "most significant issues" of the year in the BIODATA form you have filled during your psychological examination conducted by FPSC prior to viva.Or the question may be asked about the Favourite Personality you have mentioned in that BIODATA Form about which you have crammed everything.
Again REMEMBER that all the questions asked during these 5 minuts are from current BURNING NATIONAL ISSUES about which even the cartmen, greengrocer etc know more than a css candidate.For example the issues discussed in the 2007 vivas were, emergency, terrorism, role of army, ban on media, grievances of baluchistan. waziristan swat and militancy etc.Now tell me what knowledge is required for CSS viva.Many years ago, FPSC used to sit Academicians of different subjects in the panel but now there is no such practice.Now GENERALISTS are sitting in the panel rather than the SPECIALISTS.
As far as written exam is concerned, CLARITY of thoughts and concepts will score well for you but if you are confused in whatever knowledge you have got and of course this confusion will not let you streamline your answers, you will lose marks.
Those who are used to cramming things will MEMORIZE one or two books because they are not clear and hence the more they read, the more they will lose.
Every Criticism is welcome provided it is constructive