As you may already know, we are working hard to improve the RadSlider in a broad way. We've fixed a lot of issues, but also added a lot of new cool features. Now it's so easy to customize and bind (in MVVM-ish way), that I've created this Windows 7 "Mixer" like example in less than an hour. I didn't change the Slider's ControlTemplate and don't have a single line of code behind.
(Please note that the new slider will be available with the beta of Q2.2011).
Download and play with the new bits.
Just play with the Sliders - note that the most left one is the Master that can "control in a way" the others.Silverlight controls are all about styling. They MUST be easy to style and easy to customize. That's why we've changed the old slider's style with new one, that is much easier to customize (due to the less code used). But also we've added a bunch of new Style type properties that will allow you to customize it without the need of changing the ControlTemplate.
MVVM is other Most important thing when we're talking about Silverlight. Each and every property must be "bindable". Here is how I've bound the Slider to the ViewModel properties.
I have one Master slider on the left and ItemsControl populated with Sliders on the right. They both are bound to ViewModel properties.
<telerik:GroupBox Header="Devices" Style="{StaticResource BorderStyle}">    <ContentControl ContentTemplate="{StaticResource SliderTemplate}" Content="{Binding MasterSlider}" /></telerik:GroupBox><telerik:GroupBox Header="Applications" Style="{StaticResource BorderStyle}" Grid.Column="1">    <ItemsControl ItemsSource="{Binding Sliders}" ItemTemplate="{StaticResource SliderTemplate}">        <ItemsControl.ItemsPanel>            <ItemsPanelTemplate>                <StackPanel Orientation="Horizontal" />            </ItemsPanelTemplate>        </ItemsControl.ItemsPanel>    </ItemsControl></telerik:GroupBox>Placing the visuals.
<Style TargetType="telerik:RadSlider" x:Key="sliderStyle">    <Setter Property="HorizontalAlignment" Value="Center" />    <Setter Property="VerticalAlignment" Value="Bottom" />    <Setter Property="TickFrequency" Value="50" />    <Setter Property="Minimum" Value="0" />    <Setter Property="Maximum" Value="100" />    <Setter Property="EnableSideTicks" Value="True" />    <Setter Property="TickPlacement" Value="BottomRight" />    <Setter Property="Orientation" Value="Vertical" />    <Setter Property="TickBarStyle" Value="{StaticResource TickBarStyle}" />    <Setter Property="TrackStyle" Value="{StaticResource TrackStyle}" />    <Setter Property="ThumbStyle" Value="{StaticResource ThumbStyle}" />    <Setter Property="TickTemplate">        <Setter.Value>            <DataTemplate>                <Rectangle Width="1" Height="20" Fill="Gray" />            </DataTemplate>        </Setter.Value>    </Setter></Style>Styling the Slider...
<DataTemplate x:Key="SliderTemplate">    <Border Margin="10 0" Padding="20 0">        <Grid>            <Grid.RowDefinitions>                <RowDefinition Height="Auto" />                <RowDefinition Height="*" />            </Grid.RowDefinitions>            <TextBlock Text="{Binding Title}"  Margin="0 10"/>            <telerik:RadSlider Grid.Row="1" Style="{StaticResource sliderStyle}"                    Value="{Binding Value, Mode=TwoWay}" />        </Grid>    </Border></DataTemplate>And the slider template...
void slider_ValueChanged(object sender, ValueChangedEventArgs e){    this.minorChanging = true;    this.masterSlider.Value = Math.Max(this.masterSlider.Value, ((SliderViewModel)sender).Value);    this.minorChanging = false;}void masterSlider_ValueChanged(object sender, ValueChangedEventArgs e){    var delta = e.New - e.Old;    this.masterSlider.Value = e.New;    if (!minorChanging)    {        foreach (var slider in sliders)        {            slider.Value += delta;        }    }}Please let me know what do you think about the new version of the RadSlider. Also note that this is preview version and may have some issues in it.
                  Miro Miroslavov is XAML enthusiast. You can follow him on Twitter at @mmiroslavov.