Hiring good people is hard. If you advertise, you face wading through dozens or hundreds of CVs trying to figure out who the best people are. If you filter CVs, then filter again through interviews, you're probably inclined to think that you're being terribly selective, and that your final hires are among an elite. People often say "we hire the top 1%".
There are several fallacies there: most obviously, it is hard to pick the people to interview on the basis of a CV, and interviewing people is a pretty hit-and-miss affair. More crucially, and less well recognised, is that you only get to pick from the people who apply, not from the whole population. Joel Spolsky's recent article does a great job of explaining this in a really clear way.
One of Joel's conclusions, which matches at least one case in my own experience, is that working with summer students (US: interns) is a good idea. This is not for the usually stated reasons (they work for peanuts! they know all the latest research! they are really gullible about working conditions!) but simply because if someone turns out to be really good, a summer work placement might be almost the last chance anyone has to hire them before they fall off the hiring radar for good.