NOTE: I'm not a SEO guy. If this post used wrong wordings, sorry for that. And, I'm not a native English speaker, don't blame my English writing :P And, I don't know whether someone has shared something similar :)
I have several pet projects hosted on github. And, I observed that Google give pretty high ranking to github repository. If a github repository has a homepage, that homepage will get benefits as well.
Thus, I carried out an experiment at https://github.com/mrkschan/github-seo-effect. I used the search terms "Github SEO effect" as the repository name and set the homepage that links to my blog post at http://mrkschan.blogspot.hk/2013/03/github-seo-effect.html
The result is pretty amazing. Here is a Google search result before I carried out the experiment (I was using Chromium private browsing, with links set to use "gl=us").
My blog post gets nowhere on the search result.
After a few days that I set the homepage to the blog post, the result becomes the following screencap.
My repository goes to the top of the search result. And, the blog post is on the first page of the Google Search :)
BTW, shall we abuse Github for SEO purpose? Try your search here: http://www.google.com/search?gl=us&q=github+seo+effect