Thanks for all of the comments/suggestions regarding the recent AC dilemma, which really boils down to a matter of conscience vs. convenience on an individual level. My roommate and I ended up opting for convenience - as did at least 5 other households in my neighborhood (we passed several empty AC boxes on our walk to purchase ours at a nearby big-box home improvement store, not to mention several already installed AC units that were running high on a not-all-that-hot day.)
Our cooling machine is mid-range on the energy star rating (although it is a higher energy star rating than a similar, yet slightly cheaper model). And while it could probably stand to be a little more secure in the window frame, it's in, and we've yet to turn on. So until it gets really hot again it will sit in our living room window, silently nagging my conscience, "do I really need the AC? really?"