I'm quite enjoying First Light and you can definitely see the GPU acceleration at work when you play color corrected clips back from Media Player.

How much GPU acceleration is in play when you preview and render with Sony Vegas? I know that Vegas uses the archaic VFW instead of the newer and more efficient DirectShow approach that every other NLE seems to have moved to. Is First Light playback still using the GPU in Vegas even though it has the VFW pipeline limitation?

Your premise is wrong. All CineForm codec color corrections are heavily optimized and threaded CPU code, no GPU involved, anywhere. While the GPUs are getting faster, the CPU has been keeping up. We till prefer the CPU only approach for codec functions, as insures the widest compatibility, and in most cases the GPU would slow us down (moving data to and from the GPU is a significant bottleneck.)

OK that makes sense. After I posted my first comment I realized that every clip can have a different set of settings. I don't think there would be any way to even do it GPU wise and keep such complete clip independence.

So then am I correct in assuming that Vegas benefits as much as any other editor would from First Light? And that the GPU power is still free for other filters within Vegas that use it (like the GPU accelerated AAV Colorlab I use on the master video bus to switch between cRGB and sRGB color)?

Yes, Vegas benefits just as well.