Just a couple of notes to keep the pot stirred.
1) I was successful in inserting a bit of brass to fill the deep scars left by someone's hacksaw in a friend's seat tube. Not that brass will have much tensile strenth at the clamp, where it matters... I don't recall for sure, but think we had to put on a patch on the outside, too. I just can't let myself get excited about this approach, but maybe I haven't been desperate enough yet.
2) I did get desperate enough once to braze something to the head of a stuck steel seatpost, to get better purchase for twisting. It worked, but that post never got used again. :-)
You know, makes you think twice about sliding that long, long, post into a frame.
Makes me really think that Cinelli's feature of reducing the diameter of the top couple of inches to 26.2 is really very smart. Below that, the post should not be in contact with the seat tube. Now, if we all just had Cinellis...
harvey sachs mcLean va
Now, I guess the only options are to saw several cuts into the seat post from the inside with a hack saw and hope that the thing just falls apart (a good chance I bet especially if I soak in more ammonia after the cuts are made). Another option is to send it out to have another Columbus tube brazed in... (a good option if anyone would even know which Columbus tube it needs.
I've had some luck with the methods everyone else suggested: ammonia, Kroil, and another penetrant:"Gibbs", air hammer(carefully applied), big old vise and twisting...but the couple times I've had to resort to cutting it out I found a Stanley brand handsaw that allows you to fit a Sawzall-type blade to be the "right tool". These blades are thicker than a hacksaw blade and available in long length for metal cutting, I suggest the bimetal type by Milwaukee or equivalent. These cut faster than a hack and don't fold up on you or flex like a noodle when you apply pressure, although the kerf is a bit wider than a hack blade. You can use a hacksaw to make the final mm of the cut if you feel the need, though I found that it was fairly easy to feel the difference of the quality of the material between the aluminum of the post and stop when I hit the steel tube. YRMV. Good luck...it feels like VICTORY when you finally get the b*stard out of there! Alan Goldsworthy San Francisco, CA