Tim Sneath just posted some tips for optimizing the Silverlight install experience:

• Use the inplaceInstallPrompt:true parameter in CreateSilverlight.js to present the Silverlight installer directly from the current home page rather than redirecting the end-user to the Silverlight site for the installer.
• Use the <div> tag into which Silverlight content is presented to create pre-install content (e.g. a static image that provides a glimpse of the final site experience when the user installs Silverlight) and present the Silverlight installer button as an overlay over that image;
• Use the Silverlight.ua.Browser property to provide guidance to the user (for example, warning them that they may not be able to install Silverlight if they are using Netscape 4.0 as their browser).
• Use a timeout delegate to see if the installation is complete, and, if so, refresh the browser automatically so the end-user doesn't have to manually hit F5 to reload the content.

To make this even easier download the "Silverlight Installation Experience Guide (Oct 2007)" that includes a whitepaper as well as two samples that illustrate best practices for creating an installation experience of Silverlight on Web pages.