Github - Checkout Someone Else's Branch
I always forget how to do this, so this is just Google fodder.
If I want to checkout a branch from someone else's repository:
git checkout -t -b $local_branch_name $remote_branch_name
The '-t' option says "track the remote branch from my branch". The '-b' option says to actually create the branch with the given name (name will be derived from $remotebranchname if omitted).
It's so simple that I don't know why I forget this, but I do. Now that I've posted this, I probably won't forget it again :)