re: IRAS-based whole-sky upper limit on Dyson Spheres
The Ring World was a partial Dyson Sphere. Seems like enough energy for an advanced civilization. I've always wondered how they dissipate the heat from the star, or is it so efficient it uses all of it with no waste heat.
I also enjoyed the Star Trek the Next Generation episode where they discovered a Dyson Sphere, and Captain Scott trapped in the recycling transporter.