I actually have an Anker Astro2 battery pack that I do use when appropriate, such as when I'm camping or on the couch and not feeling like being stuck to the wall but also not in need of a "quick charge." The removable battery allows my son to be out with his friends doing whatever, come home, swap batteries and head out to the mall. It allows me to have the immediate ability to swap to a fresh battery when I didn't have the chance to be wired to something while I was out and about.
One upcoming specific need is an all-day tailgating event. I don't want to walk around taking pics, video and text and have to have the battery pack strapped to me/my phone. Instead, I have it in the car feeding my extra battery. Thus, when my phone drains, I can quick-swap the battery and let the drained one recharge whilst I move along with my freshly charged phone. I have a VZW Galaxy Nexus and the tailgating is in an area with weak signal (for the Gnex, anyway), so the battery will be drained very quickly. <sigh>
I totally agree that the portable power packs have done a great deal to minimize the need for removable batteries but, for my family, it hasn't quite solved the convenience issue a removable battery allows.