step-keep.js

var getFiles = Step.fn(
  function readDir(dir) {
    this.keep(dir);
    fs.readdir(dir, this.parallel());
  },
  function readFiles(err, dir, results) {
    if (err) throw err;
    // Create a new group
    var group = this.group();
    results.forEach(function (filename) {
      if (/\.js$/.test(filename)) {
        fs.readFile(dir + "/" + filename, 'utf8', group());
      }
    });
  }
);

getFiles(__dirname, function(err , files) {
  if (err) throw err;
  console.dir(files);
});

Actually, this isn't a bad idea. Also we can maybe merge this and this.parallel() since they do the same thing in the single case. People are constantly confused by the difference between this.parallel() and this.group(). Having one less API point may help the confusion.

Merging this and this.parallel() would be fantastic. The fact that you'd have to use this.parallel() when using this.keep() was a concern of mine, since it'd be a potential pitfall for users.