I really don't have much to contribute to this conversation.
I just want to post in the same thread with Sheldon Brown.

Sheldon Brown's essays on fixed gear bicycles ignited my initial interest.
I have since read every word Sheldon has written on the subject, I think.
I've tried, anyway.

So, from Sheldon's site:

http://sheldonbrown.com/gears/

Make sure to enter the correct tire size, crank length, and select gear inches (my preference).

For the winter I ride a 53X19 with 700X23 tires and a 170mm crank length for 73.3 gear inches.
This allows me to ride on frosty roads without using the front brake (although I have one).
I don't skip or skid.
I just stop.
I can do that at 73".
Too bad I don't skip or skid, because 53X19 gives me 38 ambidextrous patches.

By the way, I use a biopace chainring because of an essay on that subject written by Sheldon Brown.
I love my biopace chainring.