need a Stevia education

Hi there. Can somebody educate me about Stevia a bit?! I know it's basically meant to be better than Sugar and artificial sweetners but can't seem to work out:

a) why it's banned in so many countries (im in the UK by the way)
b) if too much of it is bad for you
c) why a previous poster (about 6/7 down the list from this one wrote 'im tired of Stevia'. Do people get 'tired' of a sweetner (indicating that there's a down side to it's usage/)

best

adam white