That is 16% of the outstanding shares being taken off the market via their buyback. Put another way, if Apples current market is sustained through the 150 million share buyback, and floor on the pps would be in place at $464. As jimturner said, not a good short right now.
Unfortunately they did this over 3 years instead of by end of year 2013. If they are bullish now is the time to put it all out there and take those shares in at todays prices. Not wait to do 20B per year only. That amounts to just 20/share per year. We all know the stock moves this much down almost every day.
150 million shares also is just 7 days trading volume. So they are going to spread that out over 600 trading days in 3 years. The market won't even feel that pull