Silverlight... Flex...
I've gotten my hands dirty with Flex 3 and didn't particularly like it. The emphasis on doing binding and pushing some of the dynamic functionality to the markup is unappealing. Furthermore, Flex, if you are not doing a mash up of services, tends to push you towards a 6-tier solution (unless you are using Adobe Air). You will need to have 3-tiers for developing your web services and a quasi-3 tiers (I managed to create 3 separate projects and link them with much effort) for your Flex application. Regardless, I didn't like it.
Enter Silverlight. I'm installing Silverlight 4 beta right now. Over the next few weeks, I plan to report back to you on how good (or bad) it is. However, Silverlight does look promising. If you are an idiot... err... I mean someone who likes to push binding to the markup it seems to support that, but it also allows you to do stuff programmatically, or so it seems. I'll let you all know shortly.
I'm still a fan of CSS/HTML/Javascript for most website development. Let's see if Silverlight can convince me the future is now.
Feeling Optimistic