To install scikit-learn easily run the following command.
curl https://gist.githubusercontent.com/dacamo76/4780765/raw/c3779996d8f6b13caaaa48d33aa1585684c7f8e6/scikit-learn-install.sh | sh
Please look over the shell file being run to make sure no evil is done to your machine.
To run it blindly just copy the command in README.md and run it in your console.
For a more detailed explanation check out my blog post http://dacamo76.com/blog/2012/12/07/installing-scikit-learn-on-amazon-ec2 which details what each step does.