Helps you to keep the number of visuals in your visual tree down

VirtualContentPresenter.cs

/// <summary>
/// Easy way to switch between no content template and some content template in silverlight
/// Helps you to keep the number of visuals in your visual tree down.
/// </summary>
public class VirtualContentPresenter : ContentPresenter
{
    public static readonly DependencyProperty VirtualContentTemplateProperty = DependencyProperty.Register("VirtualContentTemplate",
        typeof(DataTemplate),
        typeof(VirtualContentPresenter),
        new PropertyMetadata(null, (o, args) => ((VirtualContentPresenter) o).VirtualContentPropertyChanged()));

    public static readonly DependencyProperty ShowVirtualContentProperty = DependencyProperty.Register("ShowVirtualContent", 
        typeof(bool), 
        typeof(VirtualContentPresenter), 
        new PropertyMetadata(false, (o, args) => ((VirtualContentPresenter) o).VirtualContentPropertyChanged()));

    public DataTemplate VirtualContentTemplate
    {
        get { return (DataTemplate)GetValue(VirtualContentTemplateProperty); }
        set { SetValue(VirtualContentTemplateProperty, value); }
    }

    public bool ShowVirtualContent
    {
        get { return (bool)GetValue(ShowVirtualContentProperty); }
        set { SetValue(ShowVirtualContentProperty, value); }
    }

    void VirtualContentPropertyChanged()
    {
        ContentTemplate = ShowVirtualContent ? VirtualContentTemplate : null;
    }
}