Are Honoris Causa degree worth as much as PhD? Lately I have seen that some people (some ex-presidents in my country and some others) have been getting the Honoris Causa degree from some universities. Some of which have never even gone to University.  I would like to know how much is that degree worth. By "worth" I mean compared to a normal achieved PhD, can an Honoris Causa graduate give lectures at a university? Can that person be called a doctor at all? Is it possible for one to get an honorary degree in science, or engineering? How much demonstrated work would it take to get one?
I think your question indicates a fundamental misunderstanding of what a honorary degree is, and who gets one. Fundamentally, an honorary degree cannot be compared to a regular PhD. All the rules for getting a PhD fly out the window, as do all the perceived benefits for doing a PhD. If you get an honorary PhD, nobody will suddenly assume that you possess the subject knowledge of the holder of a regular PhD. 

Similarly, you seem to assume that an honorary degree is somehow an easy way towards a PhD. This is not the case. By and large, by the time you get an honorary degree, you either already have enough degrees or you will never need one again in your life.


  Can that person be called a doctor at all?


Yes, as long as you don't pretend to have a "regular" PhD.


  can an Honoris causa graduate give lectures at a university? 


Sure. Everybody can give a lecture given that he gets invited or appointed to do so. In the usual case, somebody important enough to receive an honorary doctorate is also somebody that an university would love to get for a lecture.


  Is it possible for one to get an honorary degree in science, or engineering


Sure.


  How much demonstrated work would it take to get one?


Usually none.