One thing I always found interesting in these discussions is how the same people who are quick to cite The Mythical Man-Month when it comes to the futility of adding new people to a late project will also claim that working 1-3 hours on some trivial problem is "doing free work" for a company. How much value do you think your 3 hours of work with absolutely no context can possibly add to the company? A company trying to get meaningful work done by secretly farming it out to interviewees is beyond ludicrous. Interviewers are only interested in finding good hires, not in conning you into doing their homework for them.
