Benchmark source http://spion.github.io/posts/analysis-generators-and-other-async-patterns-node.html
$ node performance.js -t 1 -n 10000 ./examples/promiseishQ.js
benchmarking ./examples/promiseishQ.js
{"time":14438,"mem":516.59375,"errors":0,"lastErr":null}

results for 10000 parallel executions, 1 ms per I/O op

file            time(ms)  memory(MB)
promiseishQ.js     14438      516.59

$ node performance.js -t 1 -n 10000 ./examples/async.js
benchmarking ./examples/async.js
{"time":876,"mem":55.0625,"errors":0,"lastErr":null}

results for 10000 parallel executions, 1 ms per I/O op

file      time(ms)  memory(MB)
async.js       876       55.06