Brake fluid has a distinctive smell. It's the most obvious when the pressure is released from the caliper when pushing the pistons out with an air compressor. Some fluid gets mixed in with the air to form a close proximation of vapor in the rush to escape. The pop of the pistons releasing from their machined hollows within the caliper are remeniscent of a far off blast. My fingers were out of the way by chance the first time the piston popped.
I set out to rebuild only one caliper. After finishing that one, the difference was significant. So much, that I decided to rebuild all of the others. It turned out that the inboard piston could be pushed out with about 20psi. The outboard pistons were not as willing, 125psi if at all. I had to resort to rust desolver in two cases. They weren't completely seized, but pretty close. The scotchbrite pad took what little hard gunk and rust there was off.
After reattaching the calipers, the front discs spin freely like a bicycle wheel. The rear ones don't (on account of the transmission). I can tell the pads aren't binding though.
I ran out of fresh brake fluid before being able to completely bleed the system, but I am excited to see how the brakes work now. They should be significantly more powerful than before.
Completed:
- Rebuilt all four calipers
The pictures:
Front caliper off the car 
View of piston with seal removed. Note the rust.
Pushing the pistons out with compressed air. The clamps prevent either piston from shooting out.
Both pistons are out, brake fluid everywhere
View inside the piston housing on the outboard side. Look at all the rust above the inner seal. 
Detail of gunk build up on rear caliper piston
Detail of piston after removing gunk with a scothbrite
Ready for reassembly, new seals and "plastilube" on the right
Close up of pistons
Front caliper reassembled and ready to be remounted on the car
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