Express + Formidable, works with bodyParser and sets req.body correctly.

.gitignore

node_modules

app.js

var Express = require('express'),
    Form = require('connect-form'),
    Upload = require('./upload'),
    app = Express.createServer();

app.use(Express.logger());
app.use(Express.bodyParser());
app.use(Form());
app.use(Express.static(__dirname));

app.post('/upload', Upload.wait, function(req, res) {
  res.send(req.body, 200);
});

app.listen(4000);
console.log('http://localhost:4000/index.html');

index.html

<form method="post" action="/upload" enctype="multipart/form-data">
  <p>Title: <input type="text" name="title" /></p>
  <p>File: <input type="file" name="upload" /></p>
  <p><input type="submit" value="Upload" /></p>
</form>

package.json

{
  "name": "express-form-example",
  "main": "./app.js",
  "dependencies": {
    "express": ">=1.0.0",
    "connect-form": ">=0.2.1"
  }
}

upload.js

exports.wait = wait;

function wait(req, res, next) {
  if (!req.form)
    next();
  else
    req.form.complete(function(err, fields, files) {
      if (err)
        next(err);
      else {
        req.fields = fields;
        req.files = files;
        req.body = extend({}, fields, files);
        next();
      }
    });
}

function extend(target) {
  var key, obj;

  for (var i = 1, l = arguments.length; i < l; i++) {
    if ((obj = arguments[i])) {
      for (key in obj)
        target[key] = obj[key];
    }
  }

  return target;
}

why do you use body decoder?