My efforts for Visual Studio 2010 support allow me to show the first screenshots:
Multiple rows of tabs in Visual Studio 2010 Beta 1
Vertical tab groups support for Visual Studio 2010 Beta 1
Default style is currently the same. In custom style I set transparent background:
<Style TargetType="TabsStudio:Tabs" BasedOn="{StaticResource DefaultTabsStyle}">
<Setter Property="Background" Value="Transparent"/>
</Style>
Tabs Studio Blog (organizing Visual Studio document tabs) 