Using app.configure in express
It is optional and remain for legacy reason, according to the doc. In your example, the two piece of codes have no difference at all. http://expressjs.com/api.html#app.configure
Update 2015:
@IlanFrumer points out that app.configure is removed in Express 4.x. If you followed some outdated tutorials and wondering why it didn't work, You should remove app.configure(function(){ ... }. Like this:
var express = require('express');
var app = express();
app.use(...);
app.use(...);
app.get('/', function (req, res) {
...
});