+10  A: 
Kent Boogaart
+1  A: 

Actually, following Kent's reply I tried this and it works fine:

<StatusBar>
    <StatusBarItem DockPanel.Dock="Right">
        <TextBlock>Go!</TextBlock>
    </StatusBarItem>
    <StatusBarItem DockPanel.Dock="Right">
        <TextBlock>Set</TextBlock>
    </StatusBarItem>
    <StatusBarItem DockPanel.Dock="Right">
        <ProgressBar Value="30" Width="80" Height="18"/>
    </StatusBarItem>
    <!-- Fill last child is true by default -->
    <StatusBarItem>
        <TextBlock>Ready</TextBlock>
    </StatusBarItem>
</StatusBar>
Afshin
@Afshin: I didn't suggest it wouldn't work, but that it's "messy and inconvenient" because it's in an illogical order, and because you have far less control over the layout. Try making the *Set* item take up half the available width and you'll see what I mean.
Kent Boogaart