Microsoft is set to launch a new version of the MSN Toolbar later today, which is powered by Silverlight. As with Adobe, Microsoft is using Silverlight in their own software - with the Toolbar being the first public use (that I'm aware of).

The toolbar requires Microsoft Internet Explorer, which is only available on Windows.

The install process is not for the faint of heart. The toolbar install page lists the following 9 steps to download the beta of the toolbar:

1. Before you can install and use Toolbar Beta, you must install Microsoft Silverlight and enroll in the Toolbar Beta program.
2. If you haven't already done so, on the MSN Toolbar Beta Download website, click Get Microsoft Silverlight, and then follow the on-screen instructions to install Microsoft Silverlight.
3. Sign in to the Microsoft Connect website with your Windows Live ID (The user name and password that you use to sign in to any Windows Live, MSN, or Office Live sites and services. If you have a Passport Network, Hotmail, or Messenger account, you can use it as your Windows Live ID.) .
4. In the left pane, click Available Connections.
5. Next to MSN Toolbar Beta, click Apply.
6. Click Continue.
7. Register with Microsoft Connect, if you haven't already done so. When your application to join the MSN Toolbar Beta program is accepted, you'll receive a notification e-mail.
8. On the Microsoft Connect website, in the left pane, under MSN Toolbar Beta, click Downloads.
9. In the list of download packages, click MSN Toolbar Beta Install, and then follow the on-screen instructions to install Toolbar Beta.

It would have been much easier for them to push the software out using Silverlight, as Adobe has done with the AIR applications on the AIR marketplace.