I can only tell you the way we do it (which is the only exposure I've had, needless to say) and I've commented on this before.
We reshuffle the deck, so to speak, immediately after each interview. The candidate pool is essentially "ranked" based on that interview day, and that rank is then folded into the bigger overall list. So, if you show-up on a day that we're interview 10 people, you'll end-up first ranked based on those 10 people. This just makes the process of stratifying you in the bigger list easier. The first person on that day is then shuffled into the pile. The second person is then shuffled below that person, and so-on. If we don't like what you're "selling", you don't get into the "willing to purchase" pile. It's just that simple.
In the big pile, the top 20 (or so) are the real standouts and everyone remembers them. The next 40-50 are a blur, and the ones below that are basically the same candidate. If you show up (at least at our program), past cycles would say that you have about a 70-80% chance of getting ranked. If you get ranked, you gotta shot. Rarely, though, as I stated do we go below 50 in our rank list (and I can't remember the last time... maybe the mid '90s... when my PD said this happened... which was a year [or two] where we didn't even fill the program).
But, just remember that if you get an interview, it means you are good enough. We weed through literally hundreds and hundreds (over 800 this year, which was actually slightly down from last year believe it or not) of applications to come up with about 250-300 invites. Out of that number of invites, we get about a little more than half who actually ever show up in person.
It's just the way it works. Again, not perfect, but it's the system we have. I'd imagine that most other programs have a similar system, because this one is so efficient and works so well. At least we've done a really good job at picking the right people since I've been around.
-copro