The current market capitalization of Apple is US$159.37 billion, squeaking by Google's market cap of US$157.56 billion. Next in Apple's sights ought to be the old man on the block, IBM. Their current market value is around US$170 billion. It may take a while for Apple to catch up with Microsoft, though -- at the present time MSFT is worth about US$255 billion.
What's your take on when Apple will overtake IBM? I'm betting on April 1st, 2009.
Financial information from Forbes.com