A bit of background: We were a group of Harvard CS-ish undergrads, had been readers of PG's essays, and also noticed a fellow classmate's startup taking off (The Facebook!). The Summer Founders Program, as it was called, was actually pretty well advertised in our community. And, from our vantage point, it seemed to be both a great opportunity and prestigious (which of course tickled our over-achieving prestige-seeking 20-year-old selves). In fact, I turned down an internship after I'd accepted the offer, to do YC (and, amusingly, after we left YC a couple of weeks in, somehow got the internship again). I remember PG asking a lot of very good questions, and poking some pretty big holes in our pitch. I'm guessing they picked us because they figured we'd pivot into something more reasonable than the idea we started on. This being the pre-smartphone era, our idea of doing something cell-phone-specific (and algorithmically focused no less) probably seemed a bit dubious.
While no one (or relatively few) may have cared in the broader investment world at the time, we -- the young hacker / startup wannabes -- definitely noticed. PG, Jessica and the rest of the team did a great job attracting our attention and interest. And that, I'd venture to say, was a key element of YC's future success that was there from the very beginning.