I've been working only on Flex projects for almost a year now, and I secretly cross my fingers and nalgas so that I won't have to go back to ActionScript only projects. I'm pretty sure that my freelance work will continue to be like that (beacuse that's all I'll consider). But I can only hope that my work at my day job (I work for Schematic) will not ocasionally revert, for some crazy (or should I say stubborn?) business requirement, to pure AS3 or (gasp!) AS2 projects.
I won't even start to talk about how Flex is a big trunk of smart, well written code that makes our lives sweeter and fun because other mighty people (Doug McCune, Ely Greenfield, etc.) are much better than me at getting that idea across. (Skeptics should check Ely's FlexBook and exegesis, Doug's TileUI prototype and maybe even listen all the way through his talk at 360|Flex in Seattle last year)
You know, all the coolest stuff that's happening out there can be easily and painlessly integrated with the Flex framework. Take Papervision3D as an example, there are many cool examples out there.
This last Sunday afternoon I sat down and wrote a DisplayObject3D viewer (super simple, but works smoothly).
This example shows bindings back and forth, component states, stock transition animations and just a little bit of styling. Check out the example at work here, and download the code from here. The mxml used for the example is here.