Joel's main goal in hiring is to get "Smart people, who get things done." (See his Guerrilla Guide to Interviewing if you haven't read it.) This makes much sense to me. Operationalizing it during interviews will mean different things to different teams and disciplines, I think. His techniques for screening developers aren't exactly the ones I'd use on UI designers, but they're not too far off. (I like giving design problems, asking for design evaluation of existing products or mockups, examples of work process and deliverables, and willingness and ability to do the boring and hard stuff in order to push work through to completion. Checking ability and interest in learning is part of this last item.)
I was talking to a friend recently about how academic journal and conference reviews are "how professionals enact their discipline," by setting up the boundaries they want on what counts as quality work and what is worth letting in to extend or challenge their field. (It takes a brave reviewer, even in a cross-disciplinary field like HCI, to recognize something from a very different perspective as a valuable contribution to the discipline.) The same could be said for the hiring process, although far less abstractly -- and it's a little more tactical. Your target processes are always going to be moving-- hopefully improving-- but you have to hire for short term success as well as investing in the future.
Hiring is hard in part because most folks aren't good at articulating what needs to get done, and how to evaluate people for those abilities. So often the emphasis ends up on wishy-washy and dangerous "cultural fit" terms, because the objective measures are missing. Performance reviews, which are obviously (or maybe not!) related to the hiring problem, are prone to the same failures; a lack of understanding of what needs to be done in an organization can lead to subjective personality measures instead of objective measures of what got done and how and what we need to do next year. (I sometimes wonder: what if, instead of the traditional performance review methods HR depts foist on us, we were to do the interview process all over again -- with a focus on what got done in the last year, instead of previous company work? No, I don't mean we fire people who get thumbs down; but we evaluate concrete work as if we hadn't spent the year with them disagreeing or drinking after hours and learning about their cheating ways or charity contributions.)
It makes sense to me that in organizations with a poor understanding of what their business is, with an incomplete understanding of how to achieve and how to measure success, you'll also find questionable (and confused) hiring and equally poor performance review processes. But in companies like Joel's that know how to measure success, hiring, retaining, and evaluation of employees is downright rational.