It's very easy to be philanthropic when you have tens of billions of dollars. To his credit he is giving it away - many people don't. What do you do with a billion dollars anyway? Never mind tens of billions...
I'd rather consider how he made those tens of billions of dollars - abuse of monopoly, some seriously underhand manoeuvres, etc. These cost people a lot, and in my opinion held the PC industry back a long time. In addition money stacked away in savings is money not circulating in the economy.
But if we consider the money paid to Microsoft for their sub-standard software and buggy Office suites as being an investment in future philanthropy, then maybe it's all okay. But in that case the people donating the money are the people who've had to use Microsoft products one way or another, and not Bill Gates.
