Possible performance improvement in descendents.

Descendents.cs

internal static IEnumerable<IPublishedContent> EnumerateDescendants(this IPublishedContent content, bool orSelf)
{
    if (orSelf) yield return content;

    Stack<IPublishedContent> nodes = new Stack<IPublishedContent>(new[] { content });
    while (nodes.Any())
    {
        IPublishedContent node = nodes.Pop();
        yield return node;

        // Preserve order.
        foreach (IPublishedContent child in node.Children.Reverse())
        {
            nodes.Push(child);
        }
    }
}

The reason is because a new IEnumerable would have to be created for each IPublishedContent visited if you used the call stack by recursively calling the method that gets the descendants - That would be inefficient. You should be able to significantly improve the traversal by using your own stack.