Turning off the image loader did the trick!  Thanks!

I couldn't get the Content property to work, though. 

Okay, here is what I've been trying to do and I think I may have uncovered a bug in the UXDesktopDockButton control:

I have a datasource with a propery of type UIElement that I'm trying to bind to the Icon property of the UXDesktopDockButton.  I created a converter that will convert the UIElement to a WriteableBitmap at the time of binding.  Now I can get the converter to work just fine on an Image control's Source property, but on the UXDesktopDockButton's Icon property I get a blank button.  See the sample code below or the attached project to recreate the issue:

Note: Ignore the bit about the DataTemplate in the converter, that code is not used yet. 

Coverter Code:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
using System.Windows.Media.Imaging;
 
namespace SilverlightPlayground
{
    public class DependencyObjectToImageSourceConverter : IValueConverter
    {
 
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            int height = 16;
            int width = 16;
 
            if (parameter != null)
            {
                if (parameter is string)
                {
                    string rawParameter = parameter as string;
                    string[] paramArray = rawParameter.Split(',');
                    if (paramArray != null && paramArray.Length > 0)
                    {
                        int.TryParse(paramArray[0], out width);
                        int.TryParse(paramArray[1], out height);
                    }
                }
            }
 
            if (value is UIElement)
            {
                UIElement element = (UIElement)value;
                if (element is FrameworkElement)
                {
                    ((FrameworkElement)element).Width = width;
                    ((FrameworkElement)element).Height = height;
                }
                WriteableBitmap bitmap = new WriteableBitmap(width, height);
                bitmap.Render(element, null);
                bitmap.Invalidate();
 
                return bitmap;
            }
            else if (value is DataTemplate)
            {
                UIElement element = ((DataTemplate)value).LoadContent() as UIElement;
                if (element is FrameworkElement)
                {
                    ((FrameworkElement)element).Width = width;
                    ((FrameworkElement)element).Height = height;
                }
                StackPanel grid = new StackPanel();
                grid.Background = new SolidColorBrush(Colors.Green);
                grid.Width = grid.Height = 300;
                grid.Children.Add(element);
                ((Grid)((UserControl)Application.Current.RootVisual).Content).Children.Add(grid);
                grid.UpdateLayout();
                WriteableBitmap bitmap = new WriteableBitmap(width, height);
                bitmap.Render(grid, null);
                bitmap.Invalidate();
                //grid.Children.Remove(element);
                Image img = new Image();
                img.Source = bitmap;
                grid.Children.Add(img);
                grid.UpdateLayout();
                return bitmap;
            }
            return value;
        }
 
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

MainPage.xaml:

<UserControl xmlns:Intersoft="http://intersoft.clientui.com/schemas"  x:Class="SilverlightPlayground.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:converters="clr-namespace:SilverlightPlayground"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
    <UserControl.Resources>
        <converters:DependencyObjectToImageSourceConverter x:Key="DependencyObjectToImageSourceConverter"/>
    </UserControl.Resources>
    <Grid x:Name="LayoutRoot" Background="White">
        <Image x:Name="BoundImage" Source="{Binding SomeUIElementProperty, Converter={StaticResource DependencyObjectToImageSourceConverter}, ConverterParameter='200,50'}"/>
        <Intersoft:UXDesktopDock>
            <Intersoft:UXDesktopDockButton Text="Test Button" Icon="{Binding SomeUIElementProperty, Converter={StaticResource DependencyObjectToImageSourceConverter}, ConverterParameter='50,50'}" />
        </Intersoft:UXDesktopDock>
    </Grid>
</UserControl>

MainPage.xaml.cs:

using System.Windows;
using System.Windows.Controls;
 
namespace SilverlightPlayground
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
            this.DataContext = this;
        }
 
        public UIElement SomeUIElementProperty
        {
            get
            {
                Grid grid = new Grid();
                TextBlock text = new TextBlock();
                text.FontSize = 12;
                text.Text = "Hello World!";
                grid.Children.Add(text);
                return grid;
            }
        }
    }
}

Thanks Jimmy.  I am aware of the application framework, and it looks good.  If I didn't already have a lot of infrastructure built in order to use Prism, I would consider it.  But I don't want to go back and rewire my platform to take advantage of the framework. 

Given that, here is what I'm doing...

I'm using the UXDesktop in conjuction with the UXDesktopDock (a.k.a. Task Bar).  I will have a "Start Menu" UXDockButton that will serve as a Prism Region.  Prism will inject the apps that my platform will provide into the "Start Menu" region.  I plan to have a DesktopManager that will handle the "Start Menu" commands to launch apps.  When an app is launched, I want to add an "Instance Button" to the UXDesktopDock that will let the user know that app has at least one instance opened.  If an app is launched with more than one instance, then the DesktopManager will add that new instance to the "Instance Button" on the task bar.  The goal is to have the task bar work like the Windows 7 task bar.  I want the users to be able to "Pin" apps to it from the start menu by dragging a copy of the button down to the task bar.  And I want them to be able to see their app instances in the task bar grouped by app. 

Does this sound feasible?  Can you see any gotchas before I head down this road?