I think it makes sense to try the least invasive methods first. Hammering, drilling and heavy levered twisting seem overly drastic unless as a last resort. Ammonia really works--I've used it on an aluminum post stuck in a rusted steel frame. Anyway, if it doesn't, no damage is done. On the other hand, applying huge leverage of one sort or another could damage the frame. Sometimes the post will rotate even though it won't come out and doing this over and over will heat the metal quite alarmingly and could distort the seat tube. Make it the method of last resort. I really wouldn't start drilling holes in a nice frame, either. You could try gently heating the seat cluster, but there's a good chance of damaging the paint, so be careful.
Bob Schenker
Oakland, CA