How do you determine if WPF is using Hardware or Software Rendering?

.NET 4.0 provides the ability to force software rendering in code:

public partial class App : Application 
{    
    protected override void OnStartup(StartupEventArgs e)    
    {         
        if (WeThinkWeShouldRenderInSoftware())            
            RenderOptions.ProcessRenderMode = RenderMode.SoftwareOnly;    
    }
}

See this post for more information.

Check RenderCapability.Tier

• Graphics Rendering Tiers
• RenderCapability Class

[UPDATE]

• RenderCapability.IsPixelShaderVersionSupported - Gets a value that indicates whether the specified pixel shader version is supported.
• RenderCapability.IsShaderEffectSoftwareRenderingSupported - Gets a value that indicates whether the system can render bitmap effects in software.
• RenderCapability.Tier - Gets a value that indicates the rendering tier for the current thread.
• RenderCapability.TierChanged - Occurs when the rendering tier has changed for the Dispatcher object of the current thread.

RenderCapability.Tier >> 16

• Rendering Tier 0 - No graphics hardware acceleration. The DirectX version level is less than version 7.0.
• Rendering Tier 1 - Partial graphics hardware acceleration. The DirectX version level is greater than or equal to version 7.0, and lesser than version 9.0.
• Rendering Tier 2 - Most graphics features use graphics hardware acceleration. The DirectX version level is greater than or equal to version 9.0.