It's official now [via SharePoint team blog]:
You may already be aware of the recent RTM announcement of SQL Server 2008. We are happy to announce that Office SharePoint Server 2007 SP1 & Windows SharePoint Services 3.0 SP1 now support SQL Server 2008. Our documentation has been updated to include support for SQL Server 2008. Please refer to:
In the next few weeks, we will publish a TechNet article that describes the benefits of running SQL Server 2008 with SharePoint Products and Technologies.