According to research firm Net Applications, U.S. Internet Web Browser Marketshare (as of May 2008):
1. Microsoft's Internet Explorer (MSFT): 74% (79% a year ago)
2. Mozilla's Firefox: 18% (15% a year ago)
3. Apple's Safari (AAPL): 6% (5% a year ago)
Data Courtesy: Net Applications
Full Disclosure: I own shares of AAPL.