As you've most likely already heard, Microsoft announced today that WinFX will target downlevel operating systems (e.g. WinXP and WS03) in addition to Longhorn. This is awesome news. For more details on our plan, I'll leave it to The Man Himself - David Treadwell. Chris Sells also has a great summarization of what this means to WinFX customers.

I'm extremely excited about this... the platform that I live, breath, and... well... y'know... eat, I guess... every day (WinFX, that is) will experience an elevated and accelerated adoption as a result. It'd be awesome if there was a simple switch we could throw that immediately gives everyone LH, but this obviously isn't reality. As a result, shipping on XP and WS03 means that we'll reach a broader audience in a shorter amount of time. ISVs and IT shops can get cooking with gas without requiring that 100% of their users be on the “latest and greatest” OS. Goodness if you ask me.

Update: Soma offers up some perspective, and Paul Thurrott gives some historical insights and opinions as to why this is a good move for the big house.