Versus Flash and AJAX
Flash is aimed at designers rather than developers, while Flex is aimed at developers rather than designers. The two can be combined, however. Flash designers may find that Expression Blend meets their needs for Silverlight development, although many Flash designers tend to be fiercely loyal to their chosen technology. Flex programmers may find that writing Silverlight XAML with code-behinds in Visual Studio is very much in the same spirit as writing MXML with ActionScript in Flex Builder; again, they may not find much enthusiasm for making that transition unless they also work on .Net applications.
Never underestimate the conservatism of children or programmers.
In my own comparisons, Silverlight 2 outperformed any of the other RIA technologies mentioned here by a significant margin, exhibiting compute and display speeds similar to those of my previous favorite, Curl. I have also seen benchmarks that came out differently; it all depends on what you measure. It is possible to overload the Silverlight 2 rendering pipeline and slow it down on some hardware. XAML enables quite a few sophisticated graphics effects that require a good GPU to achieve decent rendering speed.
Much has been made of the large installed base of Flash plug-ins. In some ways, this isn't terribly important. Silverlight's download footprint is not so big as to present a barrier to first-time users, at least for broadband users. Nevertheless, I asked my friends at PC Pitstop to give me a comparison of Flash installations and Silverlight installations. In September, Flash was installed on more than 90 percent of the roughly 75,000 distinct computers that tested at the site, while Silverlight was installed on roughly 33 percent. It will be interesting to monitor the Silverlight 2 uptake over the next few months as more applications that use it are rolled out.
When Silverlight was introduced, some pundits thought it might be Microsoft's "Flash killer." I don't really think that's the case, for two reasons. One is that many organizations have an existing investment in Flash video servers. The second reason is that Flash and Flex designers and developers tend to be very comfortable with their tools and loyal to Adobe. They don't really care whether Microsoft has something better for them, because they're too busy chopping down trees to trade their axes for chainsaws, especially when they're good with their axes and haven't learned to use chainsaws.
Nevertheless, Silverlight has substantial technical merit and relatively good performance. It's a very capable RIA technology that's especially useful in the hands of programmers with .Net experience and designers with XAML experience.