I'm not sure what point you're trying to make with the 4-hour test anecdote. But I think most people here would agree a warm body has more potential for harm than a cold seat when it comes to software developers. However you want to ensure you don't get a problem employee, whether it's with 4-hour tests or whatever, it is definitely a good practice regardless of how badly you need to hire someone.

Also, I completely believe that it's too hard to find good developers. I'm not sure if I've just been unfortunate due to industry or geography, but I know very few people I can recommend with confidence. And I have seen all kinds of mediocrity trying to pass as software developers. The places I have seen are the stuff TheDailyWTF is made of.