SQL Server 2008 is released but a lot of users who have installed Visual Studio 2008 are having problems installing SQL 2008. 

The error message a lot of users are seeing is :

Rule "Previous releases of Microsoft Visual Studio 2008" failed.

A previous release of Microsoft Visual Studio 2008 is installed on this computer. Upgrade Microsoft Visual Studio 2008 to the SP1 before installing SQL Server 2008.

The SQL Server 2008 Release Notes which can be found here has the updated information on how to proceed further with the install.
KB 956139 talks about the issue and can be found here...

If you have Visual Studio 2008 (RTM) version installed do the following:

1. Wait till the release of SP1 for Visual Studio 2008. Due next week
2. Uninstall all VS 2008 components and then install SQL 2008.
3. Install SQL 2008 components that don't require VS 2008.