One thing I missed after switching to git from svn was the ability to checkout a single directory.

Well, it seems that the ability to partially checkout a repository was added to git in February of 2012, and I am way behind.

Here is how you perform a sparse checkout:

# Initialize
git init [repo]
cd [repo]

# Fetch 
git remote add -f origin [url]

# Configure
git config core.sparsecheckout true
echo "path/to/dir" >> .git/info/sparse-checkout
echo "path/to/some/file" >> .git/info/sparse-checkout

# Checkout
git pull origin master

If you modify .git/info/sparse-checkout, you will want to run the following to update your working directory:

git read-tree -m -u HEAD