Removing dents with dry ice is absolutely possible. It takes a bit of time (about 15 minutes), but I have seen it done. I believe I saw an article on a dry ice website. It involves cooling the dent, then applying heat. The process pulls the dent right out. It's pretty cool.

I tried this with some success on small dents. I left my Accord out on a very hot day, it was about 90 degrees (F) outside. Small dents were taken out in about five minutes. Use big thick padded leather gloves and patience. This takes a while to work. Also, I just used the pops-a-dent today and was happy with the results. This also takes practice to get used to. Read the directions carefully, and most dents will come out. Mine had small, medium and large sizes available. Some hard to get dents might take two uses to get out. All in all, you can pay the big bucks and get it done professionally, or go with Dry Ice or a dent remover. I chose the latter since my car is getting painted next year, so this year I am experimenting with all of the ideas in these forums. I hope this helps and good luck!