My concern is that novice users will turn their back to a website which asks them to install Silverlight.
One of the reasons I think they might be scared of installing Silverlight is because they are not aware of what Silverlight actually is.
What's your take on this?
They do not know what is is, marketshare is around 40%. I'd say it's not ready if you want to reach everyone.
However if Flash or javascript is not an option, give a firsttime visitor window informing your clients about silverlight.
I think you're going to have a lot of users on the public internet that don't have it installed. If you're really going for a mass-market site, and you aren't doing a crazy amount of media-rich type content, I would go with something like JQuery to make your Javascript easy and cross-platform.
Well Silverlight is installed on about 50% of pc's now. So it depends on your market. Normal web users (ie. non-developers) tend to install anything you prompt them to if you can clearly and succinctly give them a compelling reason to run your application.
It doesn't tend to matter outside of the work place environments if you use silverlight or flash. What's more important is that your application will solve a problem the user has, and you can communicate that well.
You can see the website riastats.com for information on install base, the main thing is if Silverlight gives an advantage such as the NBC Olympics coverage in United States uses Silverlight because of the Smooth Streaming technology plus the ablity to have a Live DVR where live streams can be "rewound" - all these features are probably better supported by Silverlight has the Client and Server ends can be well integrated (with Microsoft solutions).
I may be a little biased as I am a Silverlight developer, but with a less than 5MB download for runtime, that helps sell it more - especially as it may be a better alternative than the Flex download for Flash if this is required to create a solution that would have worked in Silverlight as it is a larger download.
Check out the silverlight.net showcase you'll see who and where it is being used - you can then make your decision based on this - rather than a few opinions (including mine!).