FWIW, did a quick test:

* `.shift` seems to do over 4,000,000 per second (shifting off an array w/ 1 element) on my local machine, similar result on Joyent vCPU (qa0)
* `_.extend` copies a small object w/ 5 keys at a rate of ~182,000 per second (i.e., takes roughly 0.055ms?) on my local machine, seems to run 75-100% faster on a Joyent vCPU (qa0)