Nik Cubrilovic at TechCrunch has one of the best writeups I’ve seen about Microsoft’s Silverlight (formerly WPF/E): Silverlight: The Web Just Got Richer. Silverlight is gunning for Flash/Flex. Flash and Flex have some huge advantages: they’re fast, tiny and installed. The “installed” part is actually not that important, as far as end-user installation goes. Installing a plugin, especially on IE on Windows, is pretty easy. “Installed” is important, though, because there are many developers who are used to the Flash/Flex systems.
Flex is being open sourced, which will only help its adoption. Flash also runs on Linux, which Silverlight does not. Seriously, though, that may not matter yet. Linux desktop penetration is still quite small.
I’m still a fan of Flex, and I’m definitely a fan of the increasingly open approach that Adobe is taking. The competition here looks like it’s going to be pretty fierce, and that can only be a good thing for the users.
Update: I forgot to mention an important other point (sorry… this post is kind of rushed…) Something that I think is seriously in favor of Flash/Flex is that the development tools are cross platform. Macs have been big in design shops for a long time, and still are. And, many of the Mac OS X “switchers” over the past few years have been software developers (go to an open source development conference like PyCon and you’ll see what I mean). The fact that I can develop Flex applications on my Mac is a big deal. And I don’t have to settle for text editors and command line compilers. The Flex Builder IDE and the full Flash environment are both available for the Mac. This is not the case with Microsoft’s tools for Silverlight.