I'm sure it is useful in some situations, particularly in big companies with a broken hiring process. I imagine 37Signals don't find it useful as they have a more effective screening process, and people coming to interview simply couldn't possibly be that bad as they're referred or they've seen some code they wrote.

If you are really faced with candidates who are incompetent (i.e. HR has filtered candidates for you based on CVs or similar), I think I'd try to automate some kind of online quiz they can go and take before they're even allowed to apply (which can include fizzbuzz or whatever little puzzles you want, checks for cheating etc) - then you can spend the phone screen or interview actually talking about interesting stuff which is in the problem domain they'll actually be tackling and finding out what they'd do with it. I just suspect these questions can be gamed and are not necessarily weeding out all the undesirables, just those who haven't done any homework on your hiring process.

I've seen people hired who talked a good game and could have passed these trivial tests without giving away that they'd just read up on likely ones, but were lacking in all the skills necessary to bring projects in on time and competently - that sort of mediocre candidate who lies about experience and knows the basics is far harder to stop.

It's interesting how different people react to IQ tests or little programming tests though - some people hate the implication of jumping through hoops, and that ability/knowledge can be reduced to such simple set of tests, and resent being subjected to them. Others really don't care and find them interesting or at worst trivial. I'd find it kind of weird trying to guess in an interview if someone who asks for say 'select the second highest number in this list' just wants a quick solution like list.sort[list.count-2] (which in the real world would be the first choice until or unless you are likely to hit major performance issues), or if they want you to write a trivial sorting algorithm for them and explain that you're familiar with the content of an undergraduate CS course.

It's also interesting seeing the range of different interview questions posted here as examples - some are trivial filters as you say, some are more involved, and some require knowledge of basic undergrad stuff, so I'm not completely sure that all of these puzzles are intended as completely trivial, there's always the temptation to elaborate them into some kind of exam (like those posted on HN a while back with maths questions) for esoteric knowledge which is frankly useless in most people's job.