app.post( "/api/users", function( req, res ) {
    var username  = req.body.username;
    var password  = req.body.password;
    var firstName = req.body.firstName;
    var lastName  = req.body.lastName;
    var email     = req.body.email;
    //Create a new instance of our model
    var newUser = new User( {
        username : username,
        password : password,
        firstName: firstName,
        lastName : lastName,
        email    : email
    } );
    //Save our new user
    //I don't know what the best way would be to send a different response within the newUser.save function based on whether or not there's an error.
    //For example, if there's an error, I could do res.send( "Error" );
    //If not, I could send res.send( "Success" );
    //But the res var doesn't exist in the scope of the callback.
    newUser.save( function( err ) {
        //Something went wrong
        if( err ) {
            console.log( "Houston, we have a problem:", err );
            return false;
        }
        console.log( "Created a new user with the name: " + username );
    } );
}