I'm no bike mechanic, so take this with a grain of salt but it is based on very recent experience and not on what I think.

Yesterday I was cleaning/greasing/adjusting a very small Kent Street Racer (12 inch tires) that my mother in law picked up for one of her grand kids. When I went to remove the quill stem I tried loosening the bolt and tapping it with a dead blow hammer (with a bit of 2x4 pine to increase target size). The wedge was frozen solidly to the tube so the bolt would not drive down. I ended up removing the bolt completely after which I was able to remove the stem (without the wedge) easily enough. As I was cleaning and repacking the headset anyway I went ahead and pulled the fork with the wedge still clinging tightly inside. I decided to try pulling the wedge rather than pushing it deeper, so rounded up a pair of vise grips to which I had previously welded a nut so they could be attached to my 6 pound slide hammer. I clamped the fork in my vise, threaded the bolt back into the wedge, attached the vise grip equipped slide hammer to the bolt and pulled the wedge right out on the first blow of the slide.

I realize that a slide hammer is not normally considered a bicycle tool, but they come in very handy for pulling stubborn parts off/out of many different things. I have never had the occassion to use this tool to pull a frozen stem or seat post but almost look forward to the day that I can give it a go. If you have access to a slide hammer you might give it a try, but do so at your own risk, I'm not sure how much damage could be done by using this tool improperly (though blood blisters do come to mind).
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