We've talked a bit about our typical traffic in the past (https://github.com/blog/1992-eight-lessons-learned-hacking-o...), but suffice to say, we host some highly trafficked sites like the Bootstrap documentation.
If your blog isn't on that scale, and conforms to our terms of service (https://help.github.com/articles/github-terms-of-service/#g-...), we generally don't enforce hard usage quotas, but if you're concerned, feel free to reach out to support@github.com any time.