I've been working with Silverlight in its various forms over the last 9 months to develop LOB apps for my employer. I've seen the framework come along from a very lightweight presentation framework to a relatively robust RIA development platform, and I can say that I'm very happy about it and impressed with the Silverlight team for their diligence. Recently, I caught a glimpse of some of the new APIs that will be available in the Silverlight 4 release, and as a business app developer I'm both excited about and impressed with the new features that will be available.
Of course, this excitement is somewhat bittersweet.
As excited as I am about Silverlight 4, I'm really dreading the process of porting my existing Silverlight 3 apps to Silverlight 4, as I'm sure some of the SL3 APIs will no longer work when SL4 is released. I'm also not too thrilled with the fact that I'll have to shell out $$$ to buy VS 2010 and yet another version of Expression Blend just to be able to build SL4 apps and/or port my existing SL3 apps.
TCO is a big issue for businesses right now, and I honestly have to say that Adobe has Microsoft beat in this department. I really like .NET development more than AS3 development for various reasons, but when it comes down to dollars and sense I'm just not sure I can keep paying for the IDE upgrades every time there's a new Silverlight release.