We know that Silverlight currently in 3.0.x version - very fast transition from Silverlight 2.0.x. For those using Windows and Mac, it will not be an issue since the runtime supports those platform. The problem is with Linux users. I know that Mono guys (through Moonlight project) are doing their best to keep it up to date with Silverlight, but unfortunately they are too much behind.
How do you offer Silverlight to clients considering that facts?
If your client base has "full support for Linux on the desktop" as a pre-req, you're really in an interesting niche -- one I'd love to learn more about, btw, but not one I've ever encountered. If you're REALLY in such a situation, I guess your only viable silverlight strategy is to limit your silverlight use to not much more than is currently available via moonlight, clearly document to your Linux-rabid clients what's missing on Moonlight for them to be able to use your latest release, and endeavor (via clients involvement, involvement of your tech people, bounties for developers that add each missing features, etc) to get Moonlight up to the level you absolutely need it to be!-)