When I was in high school, I thought I wanted to a high school teacher. One of my teachers at that time told me and many others with similar ambitions NOT to do so if we could stomach doing anything else. His rationale was this: that we wanted to be high school teachers simply because it was one of the only jobs we'd ever seen "close-up." We thought we should be teachers because we'd spent the majority of the last twelve years of our lives watching teachers do their jobs and it was a system and a routine that we understood. It was a safe choice.
In many ways, academia lures a lot of success-driven, structure-oriented people because it's a path that seems very friendly to us. We've spent so much of our lives in an educational setting, jumping from one institution to the next, and it's what we understand. And the sheer amount of "I'm applying to grad school because what else can you do with a BA in English?"-type comments we see around here illustrate the fact that without the structure of academia, many of these great students have no idea what to do with themselves.
I'm really glad you posted this because I think it will be useful for a lot of those applying now and in the future. But also because I think that it's a good idea for applicants to reflect on whether they're applying to grad school just because it seems like the thing to do next. Especially since spending a life in academia nowadays - while perhaps a choice with structure - is not by any means a safe choice. A lot of us will never get a TT position, ever. So, if you're going to piss away the next seven odd years of your life on a PhD, it really should be because you'd rather do that and wind up with absolutely nothing than have everything but.