I'd like to share some git aliases that you might find useful if you handle pull requests from others.
Add these to your ~/.gitconfig in the [alias] section:
copr = "!f() { git fetch -fu origin refs/pull/$1/head:pr-$1; git checkout pr-$1; } ; f"
prunepr = "!git for-each-ref refs/heads/pr-* --format='%(refname:short)' | while read ref ; do git branch -D $ref ; done"
Now you can "git copr #{pr_number}" (check out pull request is the mnemonic) and it will pull down the PR in a local branch of pr-#{pr_number} and check it out for you. To do it right, you must pronounce it "Copper" with a James Cagney gangster accent.
And if you use this regularly, you're going to end up with a bunch of pr-* local branches, so "git prunepr" will get rid of them for you.