I've got an 80s TrueTemper Schwinn frameset that I picked up off of Freecycle some months ago. The bike had obviously been left outdoors for a long time, and the stem and the steatpost are S-T-U-C-K.
After soaking them down with penetrating oil for a few months, they're still not budging. Following Sheldon's advice, I used the (cheap) saddle as a wrench to apply torque to the seatpost... destroying the saddle by bending the rails.
I've acquired a few pounds of dry ice. I packed the seat tube and steerer with that material and waited until ice began forming on the outside of the tubing... it still won't budge. I'd been hoping the greater thermal contraction of Aluminum would pop them loose. We did manage to destroy the vice at the LBS, but the seatpost remains fixed.
As a last attempt, I re-cooled the seat tube and then thermally shocked it by pouring boiling water over the outside (with the cold on the inside) while applying torque to the seatpost. No progress.
Since it's winter, the leftover dry ice will last longer than normal outside in my cooler... I might still have a bit left after work tomorrow. Before I offer it up on Freecycle (to someone with the patience to saw them out with a hacksaw blade), does anybody have any other ideas that I might try?