In the less-than-three months since Apple first passed Wal-Mart to hold the third highest market capitalization among U.S. companies, Apple's stock price has continued to increase while second-place Microsoft has seen its shares drift downward.
Market capitalization is a popular metric for assessing the size of a company as a representation of the investing public's notion of the company's worth. The figure is derived by simply multiplying the number of outstanding shares of the company's stock by the share price.
Many of you probably don't remember a world where Apple was very seriously on the brink of being done and was the butt of many jokes in the computer sales world. Quite a turn around.
Apple does a great job of generating a large amount of mind share (i.e. it feels like everyone has a Mac/iPhone/etc. when they are still actually in the 8%-12% market share) so it seems like it would be obvious and a given that Apple would be doing better than Microsoft.