Note: This document is work-in-progress. Please don’t publish it on news sites, or otherwise link to it in public without the author’s permission. Private linking is acceptable.
Joel on Software and others have written about the importance of having very good developers. See for example his “Guerilla Guide to Interviewing”. Bad programmers will create code that’s buggy, insecure, hard-to-maintain, etc. The so-called “Medium-level techs” will probably not, but will be heavily under-productive in comparison to star programmers. (And according to Brooks’ Law, you can’t effectively replace one good programmer with many worse ones.)
As I noted there are many aspects that qualify someone as a good programmer. However, it does not change the fact that hiring a large number of mediocre programmers will never be as effective as hiring one or two good or very good programmers.