Facebook’s Mark Zuckerberg and his wife Priscilla Chan this week created a stir when they were reported to have pledged to give away 99% of their shares in the company — worth according to themselves $45bn — to good causes, when they announced the birth of their daughter Max (Maxima). Amidst all the bad news this good news got a lot of attention and it may seem churlish to undermine it. However, the truth is that the Facebook founder effectively pays no income tax and the shares are not being given to a charity.