The key difference I have noticed is the ice up factor. If you fish outside at all, which if you are employing modern ice fishing techniques you have to at some point, water freezing to your line is a huge deal. The ice lines do a much better job of keeping the ice off of your line and your lure in the water. More time in the water equals more potential for catching fish.

My personal favorite is Trilene Micro Ice, but I've heard good things about the Gamma series of lines also. If you are going to be inside Berkley Fireline Ice or Stren MicroFuse Ice is a good bet, but tend to ice up a bunch in cold weather.

What are your experiences with lines made specially for ice fishing?