In response to brutha
's 'What can a single sane person do with more than a billion dollar?
While I agree with the sentiments in the writeups above, I would like to point out one thing about a lot of the wealth that is mentioned above - it is paper profit.
If the above mentioned people are like any other executive of a major corporation, they will no doubt have a large mega million dollar salarly. However, they will also have large share and/or share option packages as well. Naturally, the value of the shares and share options are calculated into their net worth, however, this isn't money that is readily available to these moguls should they suddenly wish to spend 20 million dollars.
For instance, share options often have a strike date - this is a date when you can 'cash in' (the actual term is vest) the options and convert them to cash or stock. Until you reach this date, the stock options are effectively worthless as a form of liquid money.
Even if the mogul has stock, he can't sell large blocks of it at once without raising questions about why the CEO is selling stock in his own company. Everyone starts getting suspicious when a CEO starts selling his own stock - they take that as a sign that the CEO knows that the company is headed for trouble and selling in advance - net effect? the share price starts sliding thereby wiping out some (sometimes most) of the value of the company and thereby the net worth of the mogul.
This is not to say that the list of people above aren't rich - they most definitely are. I'm just commenting not to view their net worth as literally $30 billion in cash - most of that will be shares and share options - effectively cash that cannot be accessed in large amounts for sometime.