Here is a quick and dirty Python script that will help you clone all the repositories, the Gists and some metadata that can be fetched over the GitHub API.
Be warned, it only fetches public repos and data and there's no error checking.
usage: gh_dump.py [-h] [--forks] [--no-gist] [--no-metadata] username Dump an user's public GitHub data into current directory. positional arguments: username the GH username optional arguments: -h, --help show this help message and exit --forks git clone also forks --no-gist don't download user gists --no-metadata don't download user metadata
Get the code at my blog post.