Looks like the tentative release launch date for SQL Server 2008 is February 27th, 2008. Along with this three-punch release launch is Visual Studio 2008 and Windows Server 2008.

Note that per the comment below and other official sources, Feb 28th, 2008 is a launch date, meaning that Microsoft will start a heavy marketing campaign (giving away free copies, perhaps, at trade shows, advertising, etc…).