Windows 7 introduced a lot of new ways for an application to give information to users. There's a thumbnail which is usually a miniaturized version of the whole application, and possible overlays of icons onto your taskbar icon (like how Outlook shows you have new messages, or Twitter shows there are new tweets) and progress bars under your taskbar icon. There are also cool ways for the user to give direction to or about the application. For example, you can right-click the taskbar to bring up a jumplist and launch another copy of the application, or another application.
Right from the beginning, some applications pushed that architecture a bit to use the jumplist to communicate with the application itself. (This requires launching some other application that communicates with the first instance.) For example, Outlook has this jumplist:
But this isn't the only way to send a command to an application from the taskbar, and it's not always the right one. Tasks are the right choice if you're willing to take on the extra work to code them up, and furthermore if they make sense even when the app isn't running yet. So in this example, Outlook, if I want to send a new message then I want to send a new message, even if that means needing to launch Outlook to do so. But what about Messenger? Here's how it used to look:
Does that make sense when Messenger isn't even running? To me, it doesn't. Here's how Messenger handles that now. There's a much smaller jumplist:
How do you set your status? With thumbnail toolbar buttons:
Sweet! Much easier to code, easy for the users to understand, and they don't clutter up the place when the app is not running. Nice decision. And keep this in mind for your own Windows 7 applications.