I don't know if this good advice for everyone looking to hire but it seems like filtering for both ability and motivation is a good idea for young, growing companies.
The problem with any discussion here on HN is that, judging by replies, many commenters feel insecure whenever an idea is proposed that they feel could exclude them from a job, even though typically these ideas do not spread, and most people need only one full-time job at a time (writing about interviewing has the same problem. See the first few paragraphs of http://steve-yegge.blogspot.com/2008/03/get-that-job-at-goog...).
I agree that if every company started this practice in the same way, applying for five jobs at the same time while currently working at one would be difficult. But it seems very unlikely that would happen in practice.