From someone who is trying Jekyll for the first time (me):
At first I thought I had to install jekyll gem, but further reading suggested that I can just git push the raw markdown to github and github will process the markdown.
I was afraid to git push too many changes. Then I remember that I can git push –force a clean repo :)
Github said that github pages refresh rate is 10 minutes per refresh. This is not true. As soon as I commit changes, I can immediately see my changes when refreshing my browser. Very nice!