404 errors?

Errors are already addressed in Express for you. In the app.js file, there is the following:

/// catch 404 and forwarding to error handler
app.use(function(req, res, next) {
    var err = new Error('Not Found');
    err.status = 404;
    next(err);
});

Then in the views/ dir, there is errors.jade.

extends layout

block content
  h1= message
  h2= error.status
  pre #{error.stack}

Simple. If you want to customize your 404 page, simply edit this view.