Before and after caolan/async (not tested yet!)

01-before.js

// $r = redis client
// $f = util.format

function createUser(username, email, password, cb) {
  $r.incr('users.count', function(err, id) {
    if (err) return cb(err)
    $r.set($f('username.to.id:%s', username.toLowerCase()), id, function(err) {
      if (err) return cb(err)
      var user = {id: id, username: username, email: email}
      getRandom(function(err, salt) {
        if (err) return cb(err)
        hashPassword(password, salt, function(err, hp) {
          if (err) return cb(err)
          user.salt = salt
          user.password = hp
          $r.hmset($f('user:%s', id), user, function(err) {
            if (err) return cb(err)
            cb(null, user)
          })
        })
      })
    })
  })
}

02-after.js

// $r = redis client
// $f = util.format

function createUser(username, email, password, cb) {
  var user = {username: username, email: email}
  async.auto({
      id: $r.incr.bind($r, 'users.count')
    , salt: getRandom
    , hashedPassword: ['salt', function(callback, results) {
        hashPassword(password, results.salt, callback)
      }]
    , storeId: ['id', 'hashedPassword', function(callback, results) {
        $r.set($f('username.to.id:%s', username.toLowerCase()), results.id, callback)
      }]
    , storeUser: ['id', 'hashedPassword', function(callback, results) {
        user.id = results.id
        user.salt = results.salt
        user.password = results.hashedPassword
        $r.hmset($f('user:%s', user.id), user, callback)
      }]
    }
  , function(err) {
      if (err) return cb(err)
      cb(null, user)
    }
  )
}

03-test.js

var async = require('async')

var delay = 1000
  , ms

function test() {
  async.auto({
      id: function(callback) {
        ms = +new Date
        console.log('>>> 1.1')
        setTimeout(function() { console.log('<<< 1.1'); callback(null, 42) }, delay)
      }
    , salt: function(callback) {
        var m = +new Date
        console.log('%sms since last call', m - ms)
        ms = m
        console.log('>>> 1.2')
        setTimeout(function() {  console.log('<<< 1.2'); callback(null, 'saxo') }, delay)
      }
    , hashedPassword: ['salt', function(callback, results) {
        var m = +new Date
        console.log('%sms since last call', m - ms)
        ms = m
        console.log('>>> 2')
        console.log('hashing with salt = %s', results.salt)
        setTimeout(function() { console.log('<<< 2'); callback(null, 'hash') }, delay)
      }]
    , storeId: ['id', 'hashedPassword', function(callback, results) {
        var m = +new Date
        console.log('%sms since last call', m - ms)
        ms = m
        console.log('>>> 3.1')
        console.log('storing id = %s', results.id)
        setTimeout(function() { console.log('<<< 3.1'); callback(null, true) }, delay)
      }]
    , storeUser: ['id', 'hashedPassword', function(callback, results) {
        var m = +new Date
        console.log('%sms since last call', m - ms)
        ms = m
        console.log('>>> 3.2')
        console.log('storing user with = %j', results)
        setTimeout(function() { console.log('<<< 3.2'); callback(null, true) }, delay)
      }]
    }
  , function(err, results) {
      console.log('%sms since last call', +new Date - ms)
      console.log('final callback err = %j', err)
      console.log('final callback results = %j', results)
    }
  )
}

test()

04-sample.out

>>> 1.1
54ms since last call
>>> 1.2
<<< 1.1
<<< 1.2
1016ms since last call
>>> 2
hashing with salt = saxo
<<< 2
1141ms since last call
>>> 3.2
storing user with = {"id":42,"salt":"saxo","hashedPassword":"hash"}
<<< 3.2
1018ms since last call
>>> 3.1
storing id = 42
<<< 3.1
1007ms since last call
final callback err = null
final callback results = {"id":42,"salt":"saxo","hashedPassword":"hash","storeUser":true,"storeId":true}

05-retest-with-0.1.16.out

>>> 1.1
7ms since last call
>>> 1.2
<<< 1.1
<<< 1.2
1014ms since last call
>>> 2
hashing with salt = saxo
<<< 2
1014ms since last call
>>> 3.2
storing user with = {"id":42,"salt":"saxo","hashedPassword":"hash"}
2ms since last call
>>> 3.1
storing id = 42
<<< 3.2
<<< 3.1
1013ms since last call
final callback err = null
final callback results = {"id":42,"salt":"saxo","hashedPassword":"hash","storeUser":true,"storeId":true}