I am really a fan of this. I was thinking of doing a video on how to design knives in sketchup but haven't done it yet. Feel free to ask questions on it (I have more experience with it than the knifemaking itself :foot

You can make a parabola like shape with some tweaking like Nathan said by doing several curves, which I like to do sometimes. I downloaded the pro version off of my "friend" in Sweden, it doesn't have many more features, but the one that I like is the ability to import and export the 3d files. That way you can sent it to somebody running auto cad (waterjet cutting would be an example) (it costs about $500usd for the pro version)