The closer your chain is to perfect, the less chance you will have to throw a chain. When I first started riding a fixed, I would break chains and occasionally through them. I remember my cog was about 15 mm off from my CR. I still rode the **** out of the bike and 99.9% of the time life was good.

My cog and CR are now dead on because of an adjustable bb. I have not broke or thrown a chain in about 4 years.

I do not know what my chainline is. I use the method Landgolier mentioned about lining up a straight edge (I use a three foot aluminum carpenters level) on your CR. This is most important to me, having the cog and CR perfectly in line.