100 pixels is just far too short for logos that aren't very wide. 

After playing around with it I think 200 pixels is a better upper bound considering the huge size of the header. It makes a huge difference with smaller square logos. It still seems to look great on phones and tablets as well.

![logo](https://f.cloud.github.com/assets/874394/2232718/0dee0f72-9b20-11e3-8522-2af1bc6f40b6.gif)